Im not sure if 6 inch would be enough? I have to buy more inline fans for other rooms "I still have more gardens to build " But I have this 8inch already, it does not have a speed controller on it, but I was also thinking about hooking it directly to our 6 inch ducting vent that goes upstairs in the main bedroom..This may be a dumb question, but if you are going to run at a reduced rate, couldn't you get a reducer and hook filter directly to the fan and then step the fan down from 8" to 6" and then use common stock products?
Im not a venting guy, my buddy is my Mr Wilson and Im like Tim "The Toolman" Taylor, he fixes what I fek up..