Have you tried searching about some speaker switches? You always have the option to run the output on your receiver in your theater room to that switch, and if you want to play music outside, just turn off the theater speakers and switch to outdoor speakers. I'm guessing there are some speaker switches with multiple speaker inputs instead of just one, but this seems like a simple fix to me. If you don't want to use speaker switches, I would just get another receiver if I were you. If I were you, I probably wouldn't wanna go all the way upstairs (assuming your home theater is upstairs (if you even have one) ) and have to switch inputs if I just quickly wanted to switch between my phone and/or FM.
EDIT: By speaker switches, I meant a switch that will choose between the first or second output.