I can tell you how I do it and maybe this works for you maybe it doesnt. My house is also an open concept house, so any speakers on are pretty much hearable from everywhere else. So I have all mine wired back to the same equipment closet and going to the same receiver which is hooked up to my living room TV. This does a couple of things, keeps everything clean and organized and gives you flexibility as far as whats on and whats not.
As far a volume, I just use an rf remote that works from anywhere in the house or controlled by my cell phone. Its simple and works just fine for me, even the outdoor speakers. If I want to play music, I stream it from my fire tv.