Its obvious that you and I have something in common; Our listening space is horizontally challenged. I would, at the very least, move the front pair of speakers so that the front edges are no less than flush with the front of your cabinetry. Take the advice given elsewhere in this post and purchase a Radio Shack analog SPL meter. A visit to Chesky Records at www.Chesky.com
to purchase the Ultimate DVD Surround Sound Sampler and 5.1 Set Up Disc will help you feel as though you've got your money's worth out of the SPL meter. There is a lot of information on this DVD in plain terms that we mortals can understand which will definitely add to your understanding and enjoyment of this curse/hobby. The 5.1 Set Up section of the DVD will help you overcome your center channel's weakness.
Remember, its not the destination, its the getting there wherein the fun lies.