Hey @FastHound,
Thanks for writing in and for sharing your report! I’ve gone through the RoonServer, RAATServer, and system logs from your Nucleus One, and I have good news about what they tell us and a clear path forward.
The short version: this isn’t a Roon configuration issue, and there’s nothing wrong with your Roon setup or the Nucleus’s audio software. The logs show that the Nucleus is never establishing a USB connection to the Gaia at the most basic hardware level, the operating system isn’t detecting anything plugged into that port at all (other than your backup stick). Because Roon can only offer you outputs that the system detects, the Gaia never appears as a selectable device. That’s why only HDMI shows up.
A couple of specifics worth sharing, because they change what’s worth testing:
The system log records a USB device the instant it’s physically connected, before any audio drivers or Roon logic get involved. For the Gaia, we see no connection event and no error of any kind. That points to the physical link itself (cable, connector, or the Gaia’s USB input not being active) rather than anything in software.
Your own test, moving the backup stick between both ports, is a smart check, but there’s a subtlety: your backup stick is a USB 3.0 device, and the Gaia is a USB 2.0 device. Those actually use different pins inside the same USB connector and cable. So confirming the stick works only proves the USB 3.0 pins are good; it doesn’t test the USB 2.0 pins the Gaia relies on. A cable with a weak or broken USB 2.0 connection would pass your stick perfectly while being completely invisible to the Gaia, which matches exactly what we’re seeing.
With that in mind, here’s what I’d suggest trying, in order:
- Swap the USB cable. This is the most likely fix and the easiest to try. Because your stick and the Gaia don’t use the same conductors, the cable’s USB 2.0 lines have effectively never been tested. A good-quality, short USB cable is the first thing I’d change.
- Check the Gaia’s power and input. Make sure the Gaia is powered on and set to its USB input before you power on the Nucleus, then start the Nucleus back up with the Gaia already running. Some USB DACs and DDCs need to be awake and on the right input when the source boots.
- Test the Gaia on a computer. If you connect the Gaia to a laptop or PC by USB and it shows up as an audio device there, we’ve confirmed the Gaia’s USB input is healthy and can focus on the Nucleus’s port and cable. If it doesn’t show up there either, that would suggest the Gaia’s USB input board itself may need attention.
If you swap the cable and confirm the Gaia works on another computer but it still won’t appear on the Nucleus, let me know, at that point the logs give us solid evidence of a potential hardware issue with the Nucleus One’s USB port, and since it’s a new unit, we’ll take care of getting that sorted for you.
The one thing that would help most right now: when you plug the Gaia into a different computer, does it show up? That single test will tell us whether we’re looking at the Nucleus or the Gaia.
Looking forward to hearing how it goes. 
