He should not need a speaker selector at all. I have the same setup, a 5.1 family room, an adjacent kitchen with 2 speakers, and 2 patio speakers. If he use a cheap amp hooked up to the X2000 for two speakers and hooks the other two up to the X2000 zone 2 amps, then all four will play the same source, whatever he selects for zone 2. If he has wall mounted volume controls, it is really easy to turn off either the kitchen or patio. If he wants the same music in the main room, he can just select the same source and that way he can get full 5.1 sound in the main room. I guess he could use the all zone stereo mode, but then it would only play out of the L/R speakers in the main zone.
Then I agree, get a cheaper 5.1 receiver like the X1000 or even the cheaper E300 for the bonus room upstairs.
Oh, the best way to set up a volume control is to turn the volume control all the way up, then use the volume control on the receiver to turn it up to as loud as you think you might want it, then just turn the volume control knob all the way down to off. A volume control can only decrease the volume, it is not an amp. That way, you now have full range control of the sound level at eye volume control and you never have to mess with the zone 2 volume on the receiver.