Thanks very much for the responses, this is very helpful.
Now I'm thinking maybe I could get away with just having the wiring installed, and do the switches/volume controls and speakers myself (please warn me if that's crazy :), which could save me several thousand dollars.
The installation sounds similar to yours Tasmi, the in-walls (maybe Paradigm AMS100?) are just for ambient non-critical listening throughout the house, the den setup with separate speakers (not in-wall) will be for serious listening, and the surround setup will be for movies. There will be an rf remote to control main volume in both systems, but is it possible to control the separate room volumes with a remote as well?
Is the wiring all done with regular speaker wire, or do I need power (or something else) to the volume control and/or switches?