Sorry, to be more specific,
1) 5 channel amp - L, C, R, and front ceiling pair, then the surround, surround back, and rear ceiling pair on the Yamaha
2) 2 channel amp - rear ceiling pair, then the rest on the Yamaha
and actually I think option 2 would sound the best due to the fact that only a single pair of speakers are being driven from a different amp and likely the least significant pair as well.