adding speakers

I’m not keen on this sort of switchbox because there is no ability to separately control Volume on each pair of speakers. Unless your speakers are exactly the same efficiency and you are the same distance from each pair of speakers, one pair will dominate. There are control boxes with a Volume control for each pair of speakers.

Another issue is that with multiple speakers there will be a ‘wash’ of music, rather than a focused sound stage. This is good or bad, depending on your personal preferences.

Finally, I don’t suggest that you attempt to simultaneously play TV through ARC and and the other speakers. There will be a slight time offset between TV audio and the other speakers. There will be no offset when playing music through all of the speakers.

My next question was regarding the volume control.  I now have my 4 floor speakers wired directly to the AMP and can adjust their volume using the Sonos app.  If I run them all through a switch, would the app no longer have volume control for the 4 floor speakers?

The Amp would still have control - but only of all four together.

A fancier switch will offer individual volume (down) control for each pair once the Amp sets the maximum level.