Craig,
those Casatunes specs sound great on paper. We have been reading paper specs for a very long time and they almost never work out the way they say.

You will be seemingly the ONLY person on this forum to use Casatunes. That should tell you something. Many of us prefer other options to Sonos but none seem to pick Casatunes.

I wish you the very best of luck and hope this works out for you but I want to tell you this is not a proper design. You have to look at the risks of botching the whole system and loosing the faith and trust of a friend.