@the bouscy,
Whilst I no longer have the devices here to physically test this, just like jgatie mentions, I too have never heard of the case where a ‘bonded’ Connect:Amp in a Sonos Home Theatre setup could be switched and used as a standalone music player - the only way I can see that happening is if the Connect:Amp was ‘grouped’ rather than ‘bonded’ as a ‘surround’ to your Playbar - in which case they would be listed as two separate rooms in the S1 Sonos App.
Either way, the new Sonos Amp performs in the same way as the older Connect:Amp as far as I’ve ever seen and the only difference in a ‘bonded’ (not grouped) HT setup is the Connect Amp needs to be wired in one of two configurations, as clearly detailed in this support document:
https://support.sonos.com/s/article/2237
The new Amp on the other-hand does not need to be cabled and will operate wirelessly.
It really sounds to me like you may have had the two Sonos rooms ‘grouped’ when using the earlier S1 setup. If not, then to be honest I’m baffled here by your comments too. 🤔??