Drivers for the basic functions (asio), plus added functionality over the years. An ADI-2 DAC bought early on is quite a different beast today due to a permanent flow of firmware improvements. I am not talking bug fixes here, but added functionality. It is not that I need it, but its really nice...
Well, not really. Just look how long RME products are on the market, when (and why) there are design changes and how long products are supported. This is second to none.
Late to the party, I know. While I have a strong preference for minimalistic setups, I use the supra in my work setup to connect PC and DAC. No technical reason. Just for the looks.
I use RMEs ASIO driver as this is needed for automatic sample rate switching. It is also a prerequisite for RME...
SHD adds analog in and out. So you might connect an analog preamp or an analog source directly. Thats smart.
In addition you can use dirac, in case you dislike GLM.
I use roon > pi3 > Matrix-X spdif3 > 8361a, which is perfect and affordable.
Used roon > pi3 > Allo Digi One > Funk casa-t > 8361a before with great results. Casa-t cable incorporates a transformer that takes care of 75>110 ohm. Still consumer voltage, though.