If you want to maintain 7.2 AND have no delay, one solution that comes to mind is an external delay line made for pro audio. I picked one up for thirty bucks a few years ago for use with a church PA system. Delaying the audio that goes to the speakers in the back of the church synchronizes that audio with the audio traveling the hundred feet or so from the front speakers.

This only works if you can get to the line level signal going into the Sonos.