I have heard of people trying to use either a mixer, or karaoke, device with a line-in connection to Sonos and not achieving the desired outcome due to buffering audio delays, but I don’t see a reason why a mixer, with optical output, wouldn’t work with the Arc.

That said, I’ve not personally tried it and not seen anyone here who may have tried it either, with the mixer mentioned. So if you do decide to give it a go, then perhaps kindly report back the outcome, or summarise any issues encountered. 

The only issue I can envisage, is if you were to perhaps want to ‘group’ (not bond) other Sonos devices with the playing Arc and the slight audio delays that would incur across the ‘other’ rooms, but hopefully the Arc/Surrounds and any Sub(s) will work okay. 

Agreed that your setup should work, but worth noting that although this is optical, it’s limited to 2 channel stereo, not an surroud sound.  I would not set this up as permanent setup, as you’ll be limiting what the Arc can do.

I actually have this machine, which theoretically should allow you to use this on this in between your source device (Apple Tv, FireTV, etc) and TV, rather then between TV and Sonos Arc.  I’m not sure I ever really set it up that way though.  Seemed easier to just use it more as a PA system than karaoke machine, connected to a portable speaker rather than connected to the TV.  It didn’t really catch on with my family though, and now it’s buried in a closet.

I don’t recommend attempting Karaoke through a SONOS system.

Regardless of how you approach this, there will be a slight time offset between the mixer output and output from the SONOS system. In my opinion, this offset will be hard to ignore in a living room setting. Playing through ARC or BEAM will minimize, not eliminate the offset. If you attempt to Group additional SONOS speakers with the ARC or BEAM, yet another, larger offset will be introduced.

This could work if you place the headphone wearing singer in an isolated area, but this is not the Karaoke experience that everyone expects.

I guess i’ll have to buy a separate speaker for my karaoke set up. thanks for all your feedback.

Another approach would be not using a microphone for the singer.