Bub, it sounds like you have alot going on there. I can offer a couple of suggestions or point out some issues as i'm sure some others will as well.
1) Your speakers are situated rather high above the average height of your ears when seated in a couch. There will be a definite 'dull' sound if the tweeters are firing too high above your ears. See if you can't put them on some chairs with some books underneath just for experimentation purposes.
Try the different heights with the M3s and see what this does to the sound. Same thing goes for the centre vp100, but you could also try to wedge a magazine or two underneath its backside atop your TV to get it angled downward more to your ear/head area.
2) Yes, the room acoustics make a huge difference. Yours is not overly large but the vaulted ceilings would probably tend to take some volume away from the overall sound. Setting up a nice little 12x12 area where your HT is located might help to 'contain' the sound somewhat. Ultimately if the room volume is just too much and you feel the sound is still too weak even when 'cranked up', you may have to move to a larger speaker. Again this is dependant on your expectation of how much you want this system to completely fill that room with sound.
3) I definitely recommend a dvd or cd player (other than a ps2) as your source for testing out all the sound. The quality should be far superior to that of the Direct TV (depending on the source) but it will also be most consistent in what you can listen to for repeated sound tests.
