If you want a good SQ response and it to still get low. You need to run Infinate baffle either through the rear deck or through the rear seats.
IDQ's are infamous for being AMAZING IB subs.
They are great subs.
Also. Whatever your friend told you. Trust me, install is about 70 percent of getting a good SQ car. This includes the type of enclosure you choose.
The w6 is a good sub, you can run that, I would recommend running it in a sealed box, made to spec. You do not have to get 8's to be SQ. People go to IASCA finals running 15's.
I will be running 1 or 2 IDQ10v3's in .6 cubes a piece. They perform amazing, A very efficient driver.
With the fact that you already have w6's, use them. Get a box built that is to the manufacturers reccomended size and you will be happy I am sure.
I see you said you are running a 3way active front end, In that case, assuming that your midbass can reproduce under 80-90 hz well, I would cross the subs over at 65-70 and let the midbass take over from there, if your front end is 2way active, I cross my subs at 70-80 and my mids at 70-80 and up.
I wouldn't recommend doing a port firing through the rear deck you can do IB tha fires through it, but ported boxes are much less efficient at a flat response than sealed or IB.