Def Tech ProCinema and the art of speaker placement in an apt. (1 Viewer)

[Kevin N]

I'm trying to get the most out of my system and decide if I need to upgrade or not. As a quick reference, I've posted a mock up of my setup. The center channel is set up with the speaker aimed at ear level, sweet spot; the fronts are aimed at the wall behind the sweet spot (about 2-3 feet). The rears are elevated about 1-2 feet in the air and aimed at eachother, per Dolby recommendation. Everything is measured off to the inch.
Also of note, I followed previous advice and have the front ProMonitors wired into the sub and then wired from there to the receiver. I have Subwoofer turned off on the receiver and the speakers set to: Front - large, center - small, rear - small. I'm using 18ga wire all the way around and have calibrated with a SPL with all channels at the same dB level outside of the sub which is 6 dB below the other channels.
The heart of my question is, are there any small tweaks, or possibly large mistakes that I've made that could be fixed to make the sound much better? I'm thinking of upgrading from my $350 Pioneer receiver to a Denon 3802; would that make a large difference (read, a noticeable difference in sound). Thanks in advance.
http://homepage.mac.com/schlep/ht.bmp
Grey wall on the right is a 'half wall.' There is a patio door behind the setup, and obviously, scale is very bad. The fronts are toed in aiming with the grey lines; it's just too hard to draw in paint. I also forgot to add that there is a full wall next to where the sub is located; it's not open there. That's the only mistake I see.
The room measures, about 14'x13'

 

[Ricky c]

I also have the def.tech. procinemas.Per def.tech. i have mine wired via sub and lfe at the same time.Also the receiver is set to sub yes.This is per Chet at Def.Tech.You also may want to toe in your mains.

 

[Mike Kao]

I would upgrade your speaker wire to oxygen free 12GA and don't take my word for it, but wouldn't it be better to directly hook up your speakers to the receiver and not piggyback through the sub? I shouldn't think the AVR-3802 should make a profound difference in sound (in fact a few have complained about it's low-quality amp), although it probably offers a lot more convenience features.