This isn’t Volumio based yet, but if its possible I’d be all for it.
I’m working on making a darkcast/icecast radio station for my lan so I can take stereo sound from a record player and turn it into a signal my Sonos can play.
I have darkcast/icecast setup (guide), but my test hardware only supports mono input.
I’ve been looking for a known good stereo ADC, but most Google searches are guides for output, not input. This post has some steps but the device was mono.
As everyone on this forum is likely audio-centric and much smarter than me, I thought this forum could help. Anyone have a ALSA ready stereo input usb ADC suggestion? I’d like to bridge price with quality, I don’t want junk, but I’m not independently wealthy either. 
Would positing a feature suggestion for input be worth it to anyone else? I’m not sure how well it fits the Volumio purpose, but having a Raspberry pi Sonos bridge would be great for me.