Hi there!
Transplanting myself over from your thread on the General A/V board
So, just to be clear, do you already have your drywall up, your soffit up and that fireplace installed? Or is that merely a preliminary plan at this point?
You said that nothing is set in stone in this basement, so I'm guessing you're willing to renovate the theater room, even if the drywall is already up. That's a good thing!
You've got some challenges here, that's for sure. And the biggest one might actually be your ceiling height, but we'll get to that a bit later.
Nothing wrong at all with a 12'-ish x 16'-ish theater, so long as what you're after is a "cozy" theater that is perfect for two people and good for three people on occasion. If you want to regularly seat more than three people in there though, you're almost certainly going to want a larger room, which would require you to use part of the area that you've marked as your "great room".
I'm looking at this a little differently than BMX. I'm seeing your theater as an entirely separate room. If the fireplace is not yet installed, you have the option to make it a completely sealed and dedicated room. It's entirely possible to put up a pony wall right under that existing header and incorporating the existing support beam in order to wall off the theater room and make it entirely self-contained and dedicated! Of course, if you do that, you have to have a ventilation/heating/air conditioning run in there. And you'll have to check with local building codes. Some areas require that any walled off room in the basement (and this would apply to that bedroom and work room as well) have its own fire escape - typically in the form of a window that is large enough to crawl through. Some areas only require that window if the basement is being designated as its own suite. But check with your local city hall before you do all of your planning. You're going to have to comply with code in order to pull your permits.
I'm no fan of vapor barrier in the basement. Far too easy to get moisture problems. I'm a much bigger fan of using rigid foam or better yet, spray foam. Spray foam really is the best because you get perfect contact with the outer foundation wall and no need for vapor barrier! Might cost a wee bit more to bring in the spray foam guys, but it pays for itself in the end
For your wall structure, just be sure to use properly treated wood or use steel. Again, not really the biggest fan of steel construction in the basement. I'd rather go with BlueWood or an exterior grade wood. Be absolutely sure to have your sill gasket under all your footers, in between the bottom plate and the concrete foundation floor!
How's your weeping situation down there? Do you have good internal weeping all around the perimeter of your foundation? If you've got good weeping, you can put rigid foam on the floor with a 2" gap all around the perimeter that you fill in with spray foam. Combined with the spray foam on the outer walls, you basically make your basement into a "cooler" that you can heat with a candle and cool with an open mini fridge!
Now to that ceiling. You've got a typical basement ceiling that is lower in height and some sections where it is "doorway height" only (6'9") already. The easiest way for you to soundproof between the basement ceiling and the floor above is going to be to use QuietRock rather than traditional drywall. You can hang QuietRock exactly like regular drywall, so you lose nothing in the way of height. You might want to go with the thickest QuietRock for maximum soundproofing, which would lower your ceiling height a little as it's 1 3/8" thick. But the other QuietRock types are mostly 5/8" thick, so no real loss of height with those at all.
The other way to soundproof your ceiling is with a "sound clip" or channel system. I particularly like the
Genie Clip system as it's easier to install and much harder to screw up and "short circuit"! The Genie Clip system will lower your ceiling height though. If you're ok with a 7' ceiling, it's fine though.
You'd want to avoid pot lights in the theater ceiling though. Putting holes in your ceiling construction is a sure fire way to let lots of sound through. As an alternative, I'd look into putting your lighting for the theater room into the soffit that goes all the way around. You could install can lights that will light the perimeter of your theater, and then have LED lights that shoot across the ceiling from the soffit-to-ceiling edge for a cool lighting effect!
You're going to need access to that water meter, so be sure you're up to code on that.
So you'll have a BlueWood frame, sitting on sill gasket with a minimum 1" air gap between the wood and the concrete foundation wall. Spray foam the outer wall, completely filling the gap between concrete and BlueWood for perfect insulation. Hopefully be able to rigid foam the floor with a 2" gap all around that you fill with spray foam. Tuck Tape every seam in the rigid foam. Lay your plywood subfloor. Install QuietRock or use the Genie Clip system on the ceiling. Install the drywall on your walls - I'd use 5/8". Leave a small gap at the wall-to-ceiling and wall-to-floor edges that you'll fill with high quality acoustic caulk. Lay your flooring. And you've now created a room that is isolated from the foundation completely.
If your ventilation and fire safety are up to code, you can put up a standard interior wall to separate the theater from the "great room" and get a truly dedicated theater. If you can't put up that pony wall, then your only real concern is going to be your bass performance. A subwoofer doesn't "know" where your theater space ends and your "great room" begins. It's just going to try and pressurize that entire space - and that's a very big room to fill at that point!
Right now, I think you've got some decisions to make before it's worth going a lot further. Is this a separate theater space? Or do you want the display visible to the great room as well as BMX has suggested?
The gear we can make fit to suit your space, but you've gotta decide what you're after with this theater. BMX is thinking more along the lines of a bar-type atmosphere for entertaining. I'm thinking more alont the lines of a separate, dedicated space for the theater only with the great room serving as your entertaining space. So we've gotta start with that basic idea first and then we'll work from there!