This is a clean, thoughtful setup. I run a Raspberry Pi server into an Audio GD DAC, and I'm very curious about roon.
Roon has a 14-day free trial, and I highly recommend signing up for that to try it out.
I have 2 unused Raspberry Pi 3, but I've never tried to install Roon on them. It should be a piece of cake though from what I've read. I believe DietPi includes an install for Roon, so that should make it pretty easy.