I like your choice of speakers. - I'm running v2 Studio 60's, CC, and surround back ADP's (Axiom M3Ti's for side surround due to space limitations on side walls). My sub is an Outlaw LFM-1, which while not necessarily an equal to the Seismic 12 is also quite a bit easier on the pocket book; it's been a great sub and gives me all I need in a 23'x17' room with 8' ceilings.

It might not hurt to fill the wall voids with whatever batt insulation you are using elsewhere, since the space may be pretty loud at times. You can get pretty sophisticated with sound isolation (decoupling walls by building a room inside a room, ...), but the cost shoots up in a hurry. You may do some research into room acoustical treatment, particularly since there are some hazards associated with a perfectly square room.

I don't have any of Outlaw's balanced cables (no balanced amps), but the Outlaw cables that I have used have treated me very well. The PCA has been a great analog cable, the PSSV was probably the best s-video cable I used, the PSC that I've used for coax digital has worked out nicely, and the PDO is better built and less expensive than the Monster and BetterCables alternatives I've owned. If you want to avoid running component to the projector, you might pick up an Oppo DVD player - its upscaling DVI output does a great job, and for only $200 or so (I think it may have gone up to $250) it is really hard to beat. I love mine .

One thought about equipment placement... Three long runs of decent heavy-gauge speaker wire may be cheaper and much less prone to difficulties than a single long DVI run (especially since the DVI spec has a limit on length before you run the risk of not being able to sustain a signal), and with the projector near the back of the room it might be less costly to locate the equipment in back. Obviously a more exotic speaker wire for the front channels would change this equation, which would fit with your current plan.