I set up a NAS on PC using OMV on Debian Jessie. Works fine. Is it technically possible (and reasonable) to install volumio on this same hardware?
Reasonable: NO (imho). I would leave my NAS on a dedicated hardware (I went this way a long time ago). So I suggest to keep the two things separate. Most important: if the data stored on the NAS is valuable to you, get a real NAS instead of a PI powered one
The OP said “PC”, not “RPi.” But I do concur with the general point that your NAS should be on dedicated hardware.
Get yourself an RPi on which to run Volumio.
I did actually try RPI as a separate DAC with volumio. It’s an AUDIOPHONICS RaspDAC:
Unfortunately I have noise on the audio signal so strong that I cannot really use it with a stereo full amplifier. Probably various reasons, e.g. one power supply for both RPI and its attached audio board.
That’s why I wanted to find out about different outputs, e.g. SPDIF on my NAS etc.
No, my NAS is a true PC-based system based on a ASRock J3455-ITX mainboard.