I've been enjoying reading your build thread, especially since your room is quite similar to mine. I'm still a ways off (I'm working on the soffits now) but I wanted to get some clarification on a couple of the issues you had.
First, the solid core door. I've got a similar door and was wondering if you had improved the sound insulation since your original post where you had leakage. I plan to do weatherstripping around the perimeter and add some sort of sill insulation - maybe even one of the "extending seals" that the Soundproofing Company offers. I am worried though, since your results match my speculation that a solid hunk of wood will be no match for the staggered-stud, double-5/8 drywall + GG + R-19 combination. There are a bunch of door threads out there, so I'll probably end up OK, but I wanted to see what you thought.
Second, ventilation. I plan on doing the same thing you are - simply moving air from the cooler finished basement space into the theater via two vent fans (one on intake, one on output). Thing is the highest-rated vent fans I can find are only about 150 cfm, where you mentioned yours is 300 cfm. What fan did you end up using? More importantly, since you said this volume wasn't enough, I'm wondering what I'll need to move enough air.
Thanks for any advice you can provide, and thanks again for the informative thread.