Speaker placement suggestions?

Hi everybody. I just bought a pair of B&W 805's on Friday and wonder if anyone has any suggestions regarding their placement in a 12 X 20 room. This is for 50% home theater & 50% music. I use a REL Strata II for the low end and a 40" t.v. sits in between the mains.The matching stands are on a wood floor, the room has a heavy 8X10 rug. Any suggestions on what crossover frequency is best? I am having trouble choosing between 49hz and 59hz. 49Hz seems a bit empty, and 59 seems a bit boomy. Is get Radio Shacks sound level meter worth using? Thanks to all.