There is a little (or a lot) of math involved in figuring out the fresh air requirements a room needs. I ended up taking some free online a/c classes to better understand static pressure, cfm, etc, etc, etc. I reached out to the best hvac company I could find locally, I read the pages of Rod's book over and over and I reached out to someone in the studio building forums for help. The plan is to tie into my central hvac system for fresh air requirements, and then install a mini-split for temperature and humidity control. Like everything else, I designed the boxes in SketchUp and refined them as needed. The final version with figures that was submitted as an addendum to my permit it below.
I had planned to use the existing trusses to mount the silencer boxes, but once built, I found the boxes weighed around 235 lbs and it would be more psf than my trusses were rated for, and this was before I accounted for the additional 3/4" sheetrock and green glue that needed to go up. The plans were changed so that the new ceiling being built would support the weight of the boxes and they would sit between the trusses in their own box to keep them decoupled from the rest of the house. Side note here... I was told by multiple people the trusses could handle the weight. People I felt should have known better. I checked with the truss manufacturer and did the math and found it was too much. I paid an engineer to look over my work and he confirmed my thoughts. The trusses probably would have held the weight just fine, but if a hurricane came through and pulled on the roof without the correct give being available, I'm sure the insurance company would not pay out if I was found to be negligent with a remodel I had done. Do the right thing if you find yourself in a similar situation.