Hey, registered here just to bump this thread because I found it in a google search. I'm also considering an ID Q 10 in an audio integrations box in my mk6. (I've heard that these boxes also fit the mk6, anyhow.)
First of all, this is really an incredibly informative thread, and I really appreciate your taking the time to document your install. It really will save me a lot of time and aggravation :w00t:
Here's my question -- would the ID Q 10 fit in this box simply by enlarging the mounting hole? Or do you also need the 1" space because of the mounting depth? All things being equal, I'd prefer to simply increase the size of mounting hole -- it would be a bit cleaner for one, plus ID recommends a sealed box on the smaller side, whereas this box is already on the high side, and the 1" spacer just makes the box bigger. In fact, I'd love to modify it somehow to do a flush mount, for a cleaner look and a box nearer the sweet spot.
I wonder if your observation that this sub seemed a lot louder than you expected is because your box + the spacer (+ the polyfill) = a box that is too big?*
*disclaimer: I am a n00b to audio installs.