i recently bought a yamaha rv905 receiver and two jmlab bookshelf speakers and have two sets of camb soundworks ensemble II satelites as well as a sony 30" hdtv tube set... i am trying to put this system all together... do i need a sub woofer or center speaker? if so budget is a concern... any suggestions...used? brands? models? i also run my musice through this as well... i wouldn'r mind bringing in a pro to help set up but if i am close, maybe just some kind words of wisdom would help... thanks