Existing whole house Sonos upgrade

I would like to integrate Sonos into my whole house audio system. What I have now is an old (and failing) Pioneer stereo receiver with a 4 zone speaker selector connected to “Speaker A” outputs. Zones 1-3 go to built-in speakers in the walls, zone 4 goes outside to a pair of outdoor speakers.

What I’d like to do is replace the old receiver with a new amp, and still use a speaker selector, wired to the speakers as they are now. The amp source would be a Sonos Connect accessing my network. What I want to accomplish is to access Pandora, Spotify, Internet Radio, and the music files on my PC, and do so remotely from an iPhone or the PC. I understand I will be limited to a single source at a time for all zones, and will have to manually select zones with the speaker selector. But I do want to be able to select from iTunes or Pandora, etc. and be able to control on/off/volume from an iPhone & PC.

My first question is will this work?

Well, that's what I thought/was hoping. A salesman is trying to sell me 4 Connect Amps, one for each zone. When I asked him about the ZP120/amp/speaker selector described above, he came up with some jibberish that went way over my head as to why it wouldn't work. If this will, in fact work, I need some guidance on choosing an amp.

Will a simple amp like this http://www.onkyousa.com/model.cfm?m=M-282&class=Amplifier&p=i work for this application? I have no clue what to look for. We listen at background music volume levels.

Can anyone confirm this amp will work before I buy it? I know nothing about amps, but I know there's a big difference in welders of a given size. They might be rated at the same amps, but some have no guts. I assume amps are the same way, but I don't know what to look for.

Multiple speakers. Current plan: Sonos ZP120 > Onkyo M-282 > Russound SDB-4.1 or NXG Technology NX-SSVC6 > 4 pairs 8 ohm speakers. Most of the time 3 Zones will be playing, and on rare occasions, all four.

I'm sorry, I have the model number wrong. I want to use a Sonos Connect to pass iTunes from my PC, and other sources such as Pandora to an amp, then to an impedance matching speaker selector, to four zones. I understand I'll have to switch the zones manually, but I want to control source and volume with an iPhone.

I never thought of this, but do you think a single Sonos Connect Amp could drive 4 pairs of speakers?

Thanks for your help!

The ZP120 is $100 more than the ZP90, the Onkyo M-282 is $230. For the net $130 difference I'm going to get the separate amp. Seems like I'd be squeezing the little 55W ZP90, while the M-282 can just idle. I decided to get a Niles SSVC4 speaker selector. The others I looked at had more buttons to push (2 source; 6 zones), and since the grandkids will be using it, I want to keep it simple.