When discussing audio servers and players for digital music, you can observe very different approaches over the years—from using and integrating specialized OEM cards (e.g., ABC PCB, later Engineered and then Wattson Audio, Stream Unlimited, bAudio, dCS…) to relying on more or less optimized PCs (e.g., Intel NUC, Roon Nucleus…) in terms of hardware (network cards, USB interfaces, etc.) and software (Windows, Linux, etc.). In the ultra-high-end segment of these optimized PCs, brands like PinkFaun, Taiko and Innuos stand out. These manufacturers have always started with off-the-shelf PC motherboards, then introduced varying degrees of modification to power supplies, cooling, networking, USB, i2S, clocks, storage—and, of course, software. In most cases, the software layer runs on a Linux-based operating system customized to varying extents. This software flexibility lets the server/streamer handle local playback via USB-connected hard drives or connect to UPnP, LMS, Euphony and even Roon servers. For the XACT S1 EVO, however, Marcin Ostapowicz (founder of JPLAY and JCAT) took a completely different path. Starting from a blank sheet, he designed this server/streamer from the ground up—freeing it from many of the pitfalls inherent in commercial motherboards, such as noisy power supplies, electromagnetic interference and inadequate isolation.

Thus, Marcin developed his new brand, XACT, drawing on the experience he gained with JCAT products (network modules, USB interfaces, power supplies, etc.). XACT’s lineup includes Streamer/Server devices (the S1 and S1 EVO), and more recently the N1 network switch, Phantom cables, and Immotus isolation feet. In that spirit, the motherboard for both the classic XACT S1 and the S1 EVO was designed completely from scratch rather than based on any commercial platform. On the software side, it runs a Linux distribution (likely Fedora) loaded at boot from an SD card in the rear panel—which can apparently be removed afterward, indicating the OS resides fully in memory. This software layer handles all I/O and also implements a proprietary server engine (rather than relying on UPnP servers like MinimServer or Asset UPnP). I’ll dive deeper into that server component later, as it requires some getting used to. The XACT S1 EVO itself sits on three Immotus CL isolation feet—each using three ceramic beads in a concept not unlike the Polish Franc-Audio design. (I was surprised upon unboxing to find the beads loose inside the carton because one foot had come unseated from its housing.) The front panel features only a single power button, which glows orange when the unit is on. Around back, aside from the IEC power inlet and the SD-card slot, you’ll find six Gigabit Ethernet ports—only port #1 is active in server mode. Three USB ports are provided: two for connecting to a DAC (one with a 5 V supply—recommended—and one without) and a third for attaching a USB hard drive. The XACT S1 (and EVO) can also operate as an Ethernet switch when booted from an SD card loaded with a switch-focused OS. In that configuration—untested here—you would plug your router into the “WAN” port and use the remaining ports as a standard switch, with the Server/Streamer functionality disabled. As you’ll have gathered, the only audio output from this server/streamer is via USB, supporting formats up to DSD 512.

In terms of the S1’s innards, beyond its bespoke motherboard you’ll find a linear power supply dedicated to both the board itself and the data-storage drive. You can choose between two drive capacities (4 TB or 8 TB), each apparently selected with the same level of care as every other component in the system. In the EVO version, you’ll also discover a 20 MHz OCXO master clock—originally developed for JCAT’s USB and Ethernet modules—alongside Phantom-specific cabling and Immotus CL isolation feet (which aren’t included on the standard S1).

You can stream files from an external UPnP server (for example, MinimServer on a NAS) or use the built-in, optimized server by loading music directly onto the internal hard drive. There are two methods for populating the internal storage:

• Connect to the XACT over the network from a PC or Mac (presumably via SMB) and copy files directly.
• Plug a USB hard drive or flash key into the dedicated HDD USB port.1. Ensure the XACT is powered off (1/ Attach your external drive 2/ Power on the XACT and the music will transfer automatically to the internal disk)

After transfer, you must power cycle the XACT—regardless of the loading method—to trigger the indexing routine. Only once this process completes will your local library appear. This workflow has room for improvement: there’s no on-screen or app-based progress indicator for USB transfers. You’re left to verify file copies manually via a network share, and the indexing itself can take 15–30 minutes. During that time, only the JPLAY iOS app’s library update status confirms that indexing has finished.

From the previous paragraph, you’ll also have gathered that the XACT server/streamer is tightly integrated with the JPLAY iOS remote-control app (available only on Apple iOS). In this setup, both the streamer function and the XACT’s internal server are automatically detected by the JPLAY iOS app. Within the app’s settings, you can choose between the XACT’s built-in server or an external UPnP server such as minimServer. Note that using minimServer unlocks features not available on the internal server—like displaying album booklets for your local tracks. I won’t detail the JPLAY iOS interface here; instead, I’ll refer you to Joël Chevassus’ excellent April 2024 article. One thing to note is that there’s no Roon or LMS support—only UPnP compatibility and the superb JPLAY iOS app, which rivals Roon in functionality, continues to evolve, and delivers a clear playback advantage. Finally, purchasing the XACT S1 EVO grants you a lifetime license for JPLAY iOS.

Listening took place on my usual system, comprising a dCS Vivaldi APEX DAC, an Ypsilon Phaethon SE amplifier, and Børresen 01 speakers. The link between the XACT S1 EVO and the DAC is made via JCAT’s Reference USB cable, whose 5 V input is powered by an LHY 5 V linear supply. Once you understand that you need to wait 15–30 minutes for the internal server to complete its indexing—likely due to the 4 TB library size—the setup proves surprisingly straightforward. Then it was time to dive into playback using local files (no Qobuz streaming for this review). Since I already run an optimized server (details here), I’ll be sharing a comparison between the XACT’s built-in server and my external AudioLinux + minimServer rig.

Playlist (Dynamic Range DR measured with DRMeter MKII) :

• Lambchop – Is a Woman – The Daily Growl – 16b/44.1kHz [DR12]
• Nils Landgren & Michael Wollny – Fragile at Schloss Elnau – Fragile – 16b/44.1kHz [DR8]
• Tamino – Live at Ancienne Belgique – Indigo Night – 16b/44.1kHz [DR10]
• David Neerman – Noir Lac – In my craft or Sullen art – 16b/44.1kHz [DR9]
• Caroline Shaw – i Giardini – The Wheel – Limestone & Felt – 24b/192kHz [DR16]
• Four Tet – Live at the Funkhaus Berlin, 10th May 2018) – Planet – 24b/44.1kHz [DR8]
• Christophe – Intime – Les Paradis Perdus – 24b/96kHz [DR10]

In comparison with my usual streaming setups—the dCS Vivaldi upsampler, the Target Diretta (Spec RMP-UB1), and the Ustara C19—the first thing that strikes me is the sheer level of detail. This is especially evident on the Caroline Shaw and Nils Landgren tracks. You experience these works anew, paying attention in ways you never have before. On other pieces that lean more on the artists’ interpretations, what really stands out is the sense of openness—particularly on Tamino’s live performance at Ancienne Belgique—and the deeply embodied delivery. You’re drawn into the performances, feeling genuine emotion in tracks like Lambchop and Noir Lac. I expected to become fatigued by so much detail, to lose the thread of the music and the performances. But that never happened. The XACT S1 EVO manages to unite the best of both worlds: razor-sharp detail and effortless musicality. Notes are presented with long, beautiful decays—all without sacrificing the clarity of their attacks.

In comparison with Diretta, the most notable difference is Diretta’s stronger presence in the lower frequencies. I didn’t investigate this further, as the XACT S1 EVO drastically simplifies the workflow compared to Diretta’s separate server/player architecture—here, XACT handles both roles seamlessly. Using my optimized AudioLinux + minimServer rig, the gap between that external server and the XACT’s internal engine is minimal. I do hear slight variances in flow and—surprisingly—bandwidth, but I can’t objectively declare a favorite. All told, the XACT S1 EVO is superbly executed, benefiting from Marcin Ostapowicz’s years of JCAT expertise in power supplies, clock design, and noise-reduction optimizations. While I can’t compare it directly to ultra-high-end systems like PinkFaun or Taiko, it easily matches—and often surpasses—my reclocked Diretta C19 setup. Its all-in-one simplicity, internal storage expandability, and the upgrade path from S1 to S1 EVO make it extremely compelling. One caveat: the seamless JPLAY iOS integration is a double-edged sword. For those committed to Apple’s ecosystem, it’s perfection—but it leaves Android users out. Personally, I abandoned Roon for focused, attentive listening with JPLAY iOS years ago (despite owning a lifetime Roon license), and I still find Qobuz Connect encroaching on that ground. In this JCAT/XACT ecosystem, everything just clicks.

Note on Streaming Sources : The listening sessions were conducted using local file streaming—either from the XACT’s internal server or an external MinimServer-based server. That said, you can also stream Qobuz or Tidal through the XACT, since all streaming is handled by the JPLAY iOS app. Personally, I find local-file playback consistently outperforms Qobuz streaming in terms of clarity and detail, which is why I default to local streaming whenever possible.

Let’s follow-up the discussions on the forum here.