I've got a 6.1 speaker set-up, so I never used the AVR300 biamp'ing to start with. I decided on the P90/3 to be able to bi-amp the front three channels, and found that the sound became more controlled in stereo. The hi and low frequencies were clearer through my B&W 603 fronts, so much so I've actually put in the bungs in the rear ports of the 603's to control the base now I can hear it better, although the room acoustics have a lot to do with that
. And in full surround mode, the centre speaker also sounds to me slightly clearer, and more defined with vocals on DVD's. I must admit I probably have a 80/20 split for movies/cd's, so the stereo isn't used that much, but the overall front stage is better to me.
I also had the spare cash saved up, (some good overtime at work
)which also helped with the decision. Plus I traded in my Arcam A80 amp to help with the cost of the P90/3 and speaker cables. Although I did have a home demo over a long bank holiday weekend before I made my mind up. And this is something I would recommend if you can get one to prove the benefit yourself