getting clear dialog is one of the biggest challenges in home theater ingeneral and partiularly whth none-standard speaker placement.
Some source material is more problematic than others. I often have trouble with the dialog on DVDs of british TV shows. I've found 2 things that help on these:
Try DTS processing istead of Dolby. It generally puts less of the sound in the center channel and helps soe with dialog.
I've also tried bumping up the center channel volume by a few DB.This seems to help a little to overcome the british penchant for mixes with overloud background music.
I doubt that either of these will fully solve your problem, but they may help a little.
Redesigning the Den sounds like a lot more fun.
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HT:
990/770
Oppo BD83SE
Pioneer Elite DV-47A
Magnavox HDMR513h DVR/DVD-R
Sony DVD megachangers-2
Sony CD megachangers-2
Monster power centers-2
Sony 48" rear projection SDTV
Roku video player
JVC AL-A158 Turntable
Polk RT-2000s,CS-650,XS-650s,RT80s
LFM-1EX
Hsu VTF-1
12" Velodyne
Family room:
OPPO 970
Sony 32" direct view HDTV
Denon 3801
Rolk RMs