You can connect up to four passive speakers to one Amp (six speakers if they are Sonos Architectural by Sonance speakers). Each Amp acts as one zone, meaning all speakers wired to a single Amp will play the same content at the same volume. If you don’t mind two rooms being in the same zone and playing the same music, then you don’t have to get eight Amps.

Are there any In-wall Volume controls for the 8-pairs of speakers?

Yes, each pair has a wall mounted volume knob.

I recommend that you pull each control and inspect its wiring and settings. Which model control is installed?

There are various names attached to the control feature, but controls can be “Impedance matching”. After proper configuration of these controls, multiple pairs of speakers can be attached to a single amplifier. Obviously all of these speakers will carry the same program. While, in theory, one could attach all eight pairs to a single amplifier, I don’t recommend this level of stacking. Including a bedroom, attached bath, and attached dressing room would be a nice stack because the same program would be appropriate in this suite. The in-wall controls must each be set for the stacking.

Edit: How many sets of wires are brought back to the potential AMP(s) location(s)?

I’d be tempted to get a multi-channel amp and use that to power the speakers.

Feed it from a Sonos Port to get your music playing.

If you do decide you’d like different music in different rooms just add a second Port and set the input channel for that amplifier to use the Port you want to listen to.