1) I'm not aware of a receiver that has A/B options that will not run both at the same time if you want.
2) I have a Russound 4.1 speaker selector that works well for my needs. I did not shop around and compare the options, I simply took what the professional installer recommended so I don't know what else is out there.
http://www.futurehomesystems.com/a500.shtml
3) Many receivers are currently available that will do two zones. If you are going to want more than that you will likely need a speaker selector of some sort. But if I could accomplish everything with simply getting a 2 zone receiver I would plan to do that rather than the speaker selector, etc.
4) Not all receivers will drive the multiple zones well when asked to do so as the resistance is very low. I had a low end Yamaha rated at 100 wpc that couldn't handle the load, but my HK AVR 235 rated at 55 wpc does very well.
So, the short answer is go with the current receiver with the A/B speakers until you upgrade and then when you do, get a multizone receiver if that will work for you geographically, etc. If not, get a speaker selector and make sure you have a good receiver/amp (similar to what is recommended for the 4 ohm M80s, stick with HK, Denon, good seperates or something that somebody here says will drive a low resistance load).
I hope that helps.
