Yes to the two points. You can set up your PC with Linux (I use Ubuntu 20.04 on a self-built media PC) and install Roon Server on it. Roon basically will expose all audio interfaces recognized by ALSA. E.g., on my PC I installed a S/PDIF bracket to output coax and TOSLINK, and both ALSA and Roon support this output, in addition to HDMI and USB.
Only make sure your sound card is supported on the Linux distro you decide to use.
Stephen, one thing to take into account is that Roon Server should be installed onto a SSD, not a spinning hard disk. This is only for the server and database, not for music files. So, make sure you install into your HTPC a 120 or 250 GB SSD just for the operating system and the Roon Core. If you want to store your music files in the same PC, install another drive. That could be a spinning hard drive or, to keep the HTPC silent, a SATA SSD.
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