HVAC baffle box design

I am currently finishing the last few tasks needed before I can drywall the basement. One of these is solving the problem of minimizing the sound that will escape the soundproof rooms through HVAC vents (both return and supply). This is proving to be one of the most technical and crucial elements of the soundproof rooms. They are airtight rooms, and so there are serious considerations to be made such as making sure there is enough oxygen supplied to the room!

Here are the steps I have taken so far:

1. Research: I have mainly read up on studio construction forums, and how other fellow DIYers have attacked the problem. Some of the best threads are: http://www.johnlsayers.com/phpBB2/viewtopic.php?f=2&t=10303&start=0 http://www.johnlsayers.com/phpBB2/download/file.php?id=20076 http://www.avsforum.com/avs-vb/showthread.php?p=21117461&highlight=hvac+vent+sound#post21117461 http://www.gearslutz.com/board/studio-building-acoustics/526036-lots-duct-questions.html http://www.gearslutz.com/board/studio-building-acoustics/543058-hvac-baffle-box-construction-plans.html http://www.johnlsayers.com/phpBB2/viewtopic.php?f=2&t=1929&hilit=silencer&start=74 
2. Conclusion of research: The main principle behind the baffle box design, is that the 2D area of the air flow path through the box should be twice the size of the duct you are connecting to. This is to allow a sufficient of volume of air to move at a slower pace through the baffle obstructions.
3. Assess the room available to place baffle boxes in the basement. Measure the external dimensions for the baffle box in each location (in my case there are 3 supply vents and 2 return vents).
4. Design: Google Sketchup appears to be the perfect tool to design these baffle boxes, to a) ensure the design meets HVAC requirements and b) make construction of the boxes easier. I have been playing around with Sketchup, and it is indeed quite easy to use. I recently discovered a great Youtube video on building a subwoofer box, that translates well to the HVAC box: http://www.youtube.com/watch?v=dyf7_SI0JUc The video references a box dimension calculator site that is quite handy: http://reaudio.com/box.php 

I plan on adding my baffle box model to the Sketchup library, as there were not any I could find therein.

I have already bought 3/4" MDF and 1" Certainteed rigid duct liner in preparation for building the boxes. 

Isolated ceiling projector mount

The home theater room will contain a ceiling mounted projector. I decided to build a mount block isolated from the joists to ensure sound doesn't travel through the ceiling into the floor above. I used a piece of 2x10 and 4 x RSIC-DC04 brackets to fix the block to the joists.

The goal is for the two layers of 5/8" drywall to cover the block, without a gap. The projector mount can then screw through the drywall and into the block. I pre-drilled a hole in the block for the HDMI and VGA cable to pass through and down the projector mount tube. The blue electrical box will house an isolated receptacle and the green low voltage box connects to a 2" conduit that goes to the equipment area.