Hey Oh, I was wondering if you ever got your setup worked out? I was reading and thinking that your good with that hood and fan, I wouldn't change it. I would use duct reducers on the hood and run 6" out of the tent. I am sure you know but make sure that your sucking cool air in and blowing over your light, also make sure this hot air is able to leave the room the tent is in. If your running CO2 then you know you need a sealed room. If not I would make sure to have a separate 6" fan pulling through the scrubber with a speed control on it. With that setup I would leave my passive intakes open and use the duct fan on the same timer as the scrubber that way your tent will be pretty cool. Your scrubber may not have to run all the time if your ambient temps starting out are low enough.
Good Luck and happy growing.
KnB