Yeah, I spent quite a bit of time working through this. Sadly, it didn't work out quite as well as I had hoped.
Here's a layout that's very close to what I have.
I built DD+GG isolated deadvents for the 8" flex for the return. With the twists and turns in the flex, I'd say there's about 8'-10' between the opening into the room, and the fan in my equipment closet. Here's the first section of the deadvent. Not installed in this pic yet, but the fan is in the left hand section.
My basement doesn't actually have a return to the HVAC unit in it. Believe it or not, there's only two returns in our house. I was skeptical, but it does work very well. I have not measured the flow from the vents.
When I planned all this, I calculated the amount of air I needed to move in order to get 4 to 6 exchanges per hour. I bought a fan for that amount of flow (440 cfm), and tried to size my opening and ducts accordingly. The thinking was I could pull a little more flow from the 8" supply to makeup for the difference in the exhaust flow. Unfortunately, the transition into the room is too abrupt, and it's causing wind noise, and I don't have enough space to put in enough duct liner to quieten it down. I added the extra return in the equipment closet to use some of the air to help slow things down, but it just causes turbulent noise in the Tee (I'm guessing there) as opposed to wind noise.
I think my only option to is to put in a fan that I can adjust the speed.Edited by J_P_A - 8/19/13 at 7:17pm