My only observation is to istall more than just two lines.I got 6 lines in my listening room,but I would suggest to go for 4 lines and preferably 20A.Therefore your electrecian should use 12/2 Romex.I read about cryo treated wire and even heavier gauge like 10 or even 8 but in my opinion 12/2 Romex is fine and as per code.In regards to Cat6 I actually installed that in my walls too,but I don't know anything about Sonos .Don'r forget to install Roxul fire & sound insulation in your interior walls before you close them,it makes a big difference.Ceilings too if you want.
George
George