hi eveyone, need advice on surrounds and bookshelf speakers. right now i have polk- rt800i's as my mains. polk- cs400i as my center. looking to upgrade my rears, which are some yamaha's. i listen to and watch music and dvd's about the same. do i go with surround speakers for both surrounds and rears, our mix it up. i have been reading some threads and noticed everyone seems to stick with one brand on speakers. something about blending? thanks for any advice.