As someone with first hand experience with both I would have to say you won't hear much of a difference in sound quality between the two but the q definitely has the ability to get louder. Both subs sound great and have an amazing low end in 2.5 cubes tuned to 30 Hz. The idmax is noticeably more efficient while the q can handle quite a bit more power. I'd go with the q because it sounds just as good and will get louder. Not to mention if you are buying new the q is cheaper.