Buy a Raspberry Pi, a HiFiBerry Digi+ Transformer and a iFi PSU and install Roon Bridge under Linux and you’re set for around € 100. Does 192 kHz, is galvanically isolated on both TOSlink AND SPDIF on RCA.
Now that Roon Bridge is out, you can make Raspberry Pi + HifiBerry based solutions for about $70-80.
Want to feed a DAC via optical or coax?
Use a Pi + Hifiberry Digi, which will output 24bit/192khz S/PDIF.
Want to feed that amp and speakers on your porch?
Use a Pi + Hifiberry DAC, which uses a 24bit/192khz Burr-Brown DAC. You can even make versions with volume control, if you want.
Note: I don’t work for Hifiberry, but I do have one at home.
That’s certainly cheap, but it looks like it isn’t Roon-native.
Why it isn’t? I am just using rassberry pi 3 with USB to my multi bit Schiit DAC and i released a laptop that was doing this , with a very low power consumption. Before using Roonbridge, on pi I tried airiply on pi which is like airport express protocol and not Apple TV, and the sound was awful. I just listen to CD flac and not have better content. Mi pi without USB adapter( we all have tons at home) did cost me $45 with case.