Originally Posted by DonH50
If you are using switch to select which room it needs to match the rating of the amplifier, whatever that is, as that sets the maximum output power to the speakers. The speakers need not have any special power rating so long as they are loud enough with the amp you get and don't distort.
If you are trying to run more than one room at once you may have a problem with the parallel speaker loads falling below the amplifier's minimum load impedance. Multi-speaker sound distribution systems often use 70V transformers, something I imagine is beyond the scope of this thread.
HTH - Don
I agree with this poster - I'm not trying to sound hostile here.
But, there are a number of home solutions that don't run 70V/100V systems for multi-speaker output (a Denon comes to mind off hand), as well as some receiver/brand specific features (for example ABus, S-AIR, or Boselink). I have no idea what the budget requirements are, but this is the Denon device that came to mind:http://www.usa.denon.com/ProductDetails/4135.asp
Something like that is designed to integrate with other components, such as an A/V receiver, alternately depending on what equipment you already have (or what you're going to purchase) there may be a manufacturer solution. Sony's S-AIR is an example - there are many accessories able to receive signals from a compatible receiver depending on what you want to purchase (Boselink offers very similar functionality with Bose components).
The concern I would have with a speaker selector is that if you want all four zones connected at once, as DonH50 said, you may present a very dangerous load to the amplifier and this could cause problems. Generally driving four pairs of speakers from a single amplifier is a bad idea unless you're driving fairly efficient speakers with a fairly powerful amplifier (most QSC products, for example).
Again, I have no idea of what the budget here is - so my suggestions may or may not be in-line with the original goal, just a few ideas I had upon reading.