I am a little concerned about all the posts that talk to the 75ms input delay.  That may be the major issue throw my way as a deal breaker but I thought I’d still ask.

I have an old ZP120 amp. 

We do a bit of karaoke at home with a little speaker with colourful light (kids love it). However, we can't get enough microphones connected for a decent singalong. 

My thought was buying a 4 way Bluetooth microphone mixer (with 6.35mm output jack), that I could connect with a 6.35mm to RCA cable, and plug that into the Sonos amp with speakers plugged in direct. 

We'd use TV to play the karaoke itself (music and lyrics) separate to this setup (alongside a disconnected whirly disco light). 

No use of the S1 app, just connectivity.

Does that sound like it would work or does someone see an issue?