Need help with a Speaker Dilemna

I have an RM 6900 set right now that I'm using for my home theater and stereo. I'm not that compulsive about speakers for home theater but I would like to upgrade for music. The dilemna is that I have a big Sony TV that's part of an integrated stand that cannot accomodate a large center channel speaker. I MAY be able to squeeze a CS10 in there but a CS20 is absolutely out of the question and I can't put it on the wall behind it as it is a wall covered in windows. So let's say I upgrade the center to a CS10. I really love the deals out there on the Monitor 70's but folks are telling me that I really can't run those with the CS10 as the center. Is that true? Of course, I could just keep the rm6900 set for home theater and buy the monitor 70's just for music and keep one set on the "A" channel and the monitors on the "B" channel but who wants 4 front speakers?! One person advised getting the Monitor 60's which have the same 5" drivers as the CS10, but people really seem high on those monitor 70's...I don't know what to do?! Also, I have a new Marantz receiver, but discovered it can't be Bi-amped. Is that necessary for the monitor 70's? The receiver is 105 watts per channel x7.