Abyss, nice setup by the way.
You sound like you covered all your bases. Boomy sub sound can be caused by a number of factors. Location, Sub Volume, Receiver level dB setting, phase/trim settings, etc... Did you calibrate your system using a SPL meter or pink noises tests. I'm glad you are able to get the sound you desire with this foam material, heck that is what DIY is all about.
If you like deep bass man, you should try to save up for a EP500, there is nothing like them in my opinion, Axiom is truely setting new standards with the 500/600 DSP controlled subs. And they go Lowwwwwwwwwwww
