I have been working the whole house sound problem for quite a while. This is my best solution so far, and I have had a lot of success with it. Please let me know what you think. I am always looking for new ideas and input.
You basically have the same two problems everyone has with house sound: amplification and input. I think its better to divide and conquer.
1. Amplification: You hook up all six sets of speakers to an Onkyo 8050, push all the buttons on the selector in, and start cranking the volume and that thing is going to be smoking. You are going to be constantly be throwing it into protect, seriously reducing the life of the amp, and pissing off the customer. I know that no sane person would do this, but you know as well as I do that the customer's 16 year old son is going to do it sooner or later....its just a matter of time. I have looked far and wide, and I have only found one line of amps specifically designed for this application that doesn't break the budget, the Episode Digital Amp line by SnapAV.
http://snapav.com/p-1181-ea-amp-8d-70a.aspx. It just solves so many problems. With a true multi-zone amp you can be cooking all six set so speakers and it will not hurt a thing. I understand that this configuration is optimized for inline volumes, but that can be worked around.
2. Input: Everyone wants wireless connectivity from network devices, ipods, and cell phones, and if you talk to them the want "push" the stream from these devices because it is an interface that they are familiar with. All the different receiver lines I would argue do not have a viable solution for this. I don't know what your experience is with Onkyo but that Ethernet port on the back is very misleading. You will only be able to stream media in a "pull" configuration using a very cumbersome remote control based interface. Some of the really high end receivers that have apps that interface over the wifi and can "push" the stream...kind off, but not on the 8050 and not on any amp that would be designed for this application. (Denon does better than Onkyo) However, the solution to the input problem gets much easier when the amplification problem is taken out of the equation. There all sorts of network and bluetooth devices that can push a stream wirelessly to a analog/ RCA output that can go right into the SnapAV amp. I like music bridges the best if the customers are laptop users.
http://www.amazon.com/Cisco-Linksys-WMB54G-Wireless-G-Music-Bridge/dp/B000E5E6KG. For the cell users Sonos is great.
http://www.sonos.com/. Air play for the Apple impaired.
http://www.apple.com/itunes/airplay/
. and so on....
Having a set up like this is also very inert to change. As tech changes two things have been very constant: speaker amplification and 8.5mm/ stereo outputs. As the next trend hits the market the customer can just swap out the input device.
BTW, standard multi-zone amps are worthless given that none come with dual DSP's. Even the flag ships.
-Hope this Helps
Joe