Polk Audio RC55i In-Wall Surround Speakers (can't...

HI- this may be a pretty elementary question and an easy question to answer but im a newbie:)
I just had 5 Polk Audio RC55i In-Wall Surround Speakers (R,L,C,SL,SR) installed in an 13x13 room and im using a Marantz SR4002 A/V Receiver. The first day i sat down to watch a movie (300 actually) i noticed i can barely hear when the onsreen actors are whispering .... basically the lows are too low and when i turn it up loud enough to hear its way loud? HELP ME:)  The speakers are mounted at the top of the room. Any advice would be GREATLY appreciated... their is nothing worse than spending a great deal of money on a system that look great and jsut doesnt sound the way that you expect it to... im sure it may have something to do with my settings but (as i said im a newbie)...and the Marantz unit while powerful is not terribly user friendly
Thanks so much HELP!