Though I would think that you would rarely use the full 600 watts of your MF A3cr, at musical peaks you probably would, especially if you like to listen loud. In that case even a P600 would not be enough, especially if you want to run other gear through it. I would strongly advise against the use of the 300, I would imagine it to seriously limit dynamics or blow a fuse, but then basically it all depends on your listening habits and how powerhungry your speakers are. Just my two cents. Cheers,