daveauk,

As a general rule you should hear improved sound with a separate amp versus the using the amp in a receiver. I don't have any experience with your Yamaha, but I base my opinion on limited testing I did with my Pioneer Elite reciever with the ATI 2005 (Outlaw 7500 clone) I'm currently using with a 990. The ATI improved the sound of the Pioneer. A few questions to consider when looking for an amp: What speakers you are using (efficiency)?; How big is your room?; How loud do you listen to movies and music?

If you are going to continue with a 7.2 system and possibly replace the Yamaha with a pre/pro, a seven channel amp might be a good choice. The power of the amp should be based upon the questions above. Should in the future you change out the Yamaha for a pre/pro with up-to-date features you'll be ready to go amp-wise.