In short: Windows 10, Big Sur on an M1 Mac and Rasperry Pi 4 all work with the UltraLite-mk5.
I’m using the UltraLite-mk5 hooked up to a Raspberry Pi 4 running Ubuntu 21.04 (Linux kernel 5.11 or later seems to be important from what I’ve read) and CamillaDSP, and this combination works just fine. No drivers are required. I’ve got CamillaDSP in place to be able to run convolution for non-Roon sources, but to play just Roon, CamillaDSP isn’t required. However, there is a small bug in that configuration that I’m just about to report (any unused channels get filled with a fairly loud static noise!).
It also works just fine on Mac or Windows too. On either platform you need to download the appropriate MOTU package which installs both the relevant drivers and also an application called CueMix 5 which allows you to configure the MOTU. Once that’s done, CueMix 5 can be closed and the UltraLite retains the appropriate settings. You can set the master volume to apply to whichever channels you like.
For completeness, I tried it with the SOtM sms200 Neo and that doesn’t work. I suspect that’s because it’s based on a Linux kernel earlier than 5.11.
I did a brief trial with a headless fanless W10 machine running RoonBridge running as a service, UEFI set to reboot on power restore after any power interruption, and that works just fine too as a reliable appliance for this purpose. I got the impression that my particular W10 machine didn’t sound quite as clear and transparent as either using the RPi4 or Mac, but since my plan was to use the RPi4 I didn’t spend much time testing that impression.
One other point. The device works at a fixed rate that you set with CueMix 5. EDIT - incorrect. see later in this thread I run mine at 192kHz but it would be perfect if it swapped automatically between that and 176.4kHz so the Roon sample rate conversion could be set to a power of 2. Of course you can swap manually if that’s really important to you.
And finally, it sounds great! But you probably know that already.