Thanks for all the info.
Well, I do hear "something" in the sub-bass range, but it is generally weak and/or muddy sounding as compared to mid-bass and I can't get equal-sounding mid-bass and sub-bass even with equalization. So maybe it is an amping problem or maybe there is really some problem with the headphones or the cable.
Generally I've read these stories (maybe even here, I don't remamber) of people using the q40s and enjoying subwoofer tests and dubstep remixes on youtube because of their bass capabilities. That is very unlike my current experience with them.
Edited by Ketill - 8/29/13 at 5:44am