Hey everyone,
I asked a question in the dedicated forum, but soon realized that it might be better asked over here as sound transmission isn't that much of a concern to me and I really just need a fix to my problem of extending the vents. Please see the link below and my question is the first post in the thread. Any advice would be helpful. Thanks.

http://www.avsforum.com/avs-vb/showthread.php?t=1188400

IF I understand, you just want to extend the existing vent from the main trunk through the drywall and into the room? Sound isolation is not an issue?

You should be able just unscrew the exisitng vent cover and remove. I think you'll find that the cover is about 1.5" thick. That should be plenty to just install your drywall, cut out the hole and replace the vent cover. You just may need to use longer screws.

IF the main truck is along the inside wall (as mine is), you may want to consider moving it, even if sound isolation is not an issue. I moved mine over to the outside wall where it really belongs for HVAC purposes (you really want to heat/cool the outside walls, not the inside walls). Fortunately, the josits ran the right way and I had enough space between the trunk and the wall to install a new take-off and run flex duct up and over the top of the tunk to the outside wall. It actually makes for 270 degrees of bend in the flex.

Good luck!

IF I understand, you just want to extend the existing vent from the main trunk through the drywall and into the room? Sound isolation is not an issue?

You should be able just unscrew the exisitng vent cover and remove. I think you'll find that the cover is about 1.5" thick. That should be plenty to just install your drywall, cut out the hole and replace the vent cover. You just may need to use longer screws.

IF the main truck is along the inside wall (as mine is), you may want to consider moving it, even if sound isolation is not an issue. I moved mine over to the outside wall where it really belongs for HVAC purposes (you really want to heat/cool the outside walls, not the inside walls). Fortunately, the josits ran the right way and I had enough space between the trunk and the wall to install a new take-off and run flex duct up and over the top of the tunk to the outside wall. It actually makes for 270 degrees of bend in the flex.

Good luck!

Yes, you understand correctly, the problem in my situation is the bottom of the finished drywall will be about 4 inches from the bottom of the main heat run. So, I have to make some type of box (from what I've found online) to extend the vent hole that is there now to the finished drywall. The main run is already on the outside wall (or pretty close).

OK, NOW we're getting somewhere!

Is it 4 inches or is 3.5 inches? If it's 3.5, I'd just build a box out of a length of 2x4 (which is really 1.5X3.5). Otherwise, I've seen 2'X2' sections of drywall at my local home Depot. I'd just measure, cut the strips and make a box out of that. Then I'd just seal them in place with some caulk.

OK, NOW we're getting somewhere!

Is it 4 inches or is 3.5 inches? If it's 3.5, I'd just build a box out of a length of 2x4 (which is really 1.5X3.5). Otherwise, I've seen 2'X2' sections of drywall at my local home Depot. I'd just measure, cut the strips and make a box out of that. Then I'd just seal them in place with some caulk.

Well...it's actually a little more than 4 inches, so I was just going to rip some 1/2 inch pine boards down and make boxes out of that, then I was going to run some 2x4 cross supports just to the outside of the current vent cut-out and attach the box to those and seal it up at the main trunk. This should give it plenty of strength and a nice solid frame for the drywall to be attached.