What's harder, optimizing hardware or software?
Software is definitely more difficult as it is far more complex. There are many more variables than in hardware.

Was it hard to integrate both?
This is the device I've worked on the most in my entire life. After more than 10 years of developing JPLAY, I saw first hand how the software has as much sonic impact as the hardware platform. Through meticulous testing I explored all possible operating system permutations and player code to identify the most harmonious combination for the S1 hardware. I hope this obsessive fine-tuning will be appreciated in the final product.

What prompted you hosting the OS on SD card not hard drive?
There are a few reasons but the most important one is that a proper SD card offers better sound quality. The S1 uses an industrial-grade SD card based on highly reliable SLC NAND. I made that selection by ear.

How did the idea of the external design come about? It's quite unusual.
It was my designer's concept. I wanted something modern and sleek. I must say that I like the design a lot.

At some point you sent me a new OS so I guess you keep working on it constantly. What were the improvements about?
I'm constantly working on it. It's just who I am. Reducing computational overhead is something that usually brings improvements and was the case with the update you received. I expect that most updates will come through the app because the XACT OS/player is already very well-optimized. At some point I'd like to add a CD-ripping feature.

Now that you already have what seems to be one of the best servers/transports to market, what's next? Do you see room for still more tweaking of the S1 or is the only way forward now to develop an entirely new device from scratch?
I am planning an S1 upgrade for next year's High End Munich show. It will include the Master OCXO Clock board we just launched for JCAT plus a few other improvements currently in R&D. All S1 are future-proof and can be upgraded.

The form factor of XACT S1 stands out from all other servers I previously hosted. Those either used generic computer chassis or custom cases designed to look similar to other components in a given company's portfolio. With the S1 being the first of its kind, there were no precedents to model and the casework is original and elegant. For me it triggers a minor vintage vibe like radios or receivers from 40 to 50 years ago. The more I lived with it, the more it grew on me. The whole fan-less design is very modern if modest to eschew all flashy or luxo elements. The chassis is aluminium with a black front featuring a single light-ring power mains which blinks orange during boot-up before it goes steady. The back features a Furutech IEC and three USB ports each with its own designation. One should be used as output into a DAC, one as input for an external drive and the last one as alternate DAC feed without 5V power. Marcin told me to use the powered port for best sound. After some listening I tend to agree but test for yourself. Next to the USB ports is the SD slot for the operating system. Alternate OS code can turn this machine into a dedicated high-end network switch or LAN distributor.

Next come six GB Ethernet ports with gold-plated high-durability EMI shielded RJ-45 connectors with built-in 12-core transformers for extra isolation. We can turn off the port LEDs to eliminate their noise. When using the XACT S1 as server, we only need the N°1 LAN port for our router or switch. Only if we convert this deck into a very expensive switch would we use all six RJ45. They space reasonably far apart to accommodate even fatter audiophile plugs. Inside one finds Marcin's pride and joy, his proprietary ZeNA (Zero Noise Architecture) motherboard. There are no switching DC-DC converters, only super-low-noise linear regulators. Combined with his own advanced power supply section based on JCAT's renowned linear OPTIMO PSU featuring a large toroidal transformer plus 140'000µF capacitance of Nichicon's flagship Muse and Fine Gold capacitors, the XACT S1 runs zero switch-mode power branches. Marcin claims that it makes his the first and only music server to do so.

There's also an extremely low-jitter Emerald OCXO clock with ±5ppb stability. It's the same as used in JCAT's XE USB/NET cards. Based on extensive listening Marcin decided that files stored on built-in SSD sound better than when accessed over LAN. Standard capacity is 4TB but for a surcharge up to 16TB are available. The internal cable connecting drive to motherboard is JCAT's top version. Operational control is via a lifetime license of JPLAY's player software. Its interface is user-friendly and operation smooth and fast. For now the only slightly annoying behaviour for a Roon user is the necessity to re-sync data each time we add new music files. Roon does so automatically to require no manual prompt. While sonics are best with high-quality files from local storage, we can stream over the local network using UPnP/DLNA. JPLAY also integrates Tidal & Qobuz for which we obviously need our own subscriptions. The S1 offers bit-perfect native playback of DSD up to DSD512 and PCM up to 768kHz at 16-32 bits. Supported file types are DSF, DFF, FLAC, ALAC, WAV, AIFF, MP3, AAC/M4A and pass-thru MQA. In the app we can filter albums in our libraries by file type, sample frequency, bit depth, genre, album, artist and so on. We can tag favourites and check most-played albums/tracks. It's a truly advanced app and unlike many others, turned out to be a pleasant experience this Roon user could get used to.