I too was a bit unsatisfied with the low end of the ATH-AD700's. I found a very cheap solution for the low end that did "dramatically" increase the bass response to an acceptable level for audiophiles. Ok, so you may want to sit down... DUCK TAPE! (Make that 1002 uses!
Yep, I couldn't find any solid film replacement earpads, so I carefully cut and shaped duck tape (the cool "raceway checkered" design, not the grey) to cover all the velour area. Of course 53mm drivers are capable of putting out plenty of their own bass signature!
I used 4 strips of duck tape on each pad, essentially 2 vertical and 2 horizontal, that wrap around the sides of the velour leaving an open square in front of the driver. Pinching/cutting any excess around the sides.
The isolation the duck tape provides definitely helps. It becomes a whole new and improved headphone. The bass was always there!!! It seals completely around the ear much better for better db pressure. And for my small head, holds the hp's on my head much better. It creates a much better chamber for the sound. IMO, MUCH better, without any loss in its other very good sound qualities. It may bring the sound stage in just a smidgen. A good thing in my book. Besides, it was open and airy enough as it were.
I wanted to add a picture or two. I would be glad to share a picture through email so someone could post it here, as "My account does not have the required permission to access [insert image] page."
*The duck tapes sticks fine to the velour and can be pulled off carefully with ease. The only exception is it sticking to the 1/2 inch thin, fragile!! pleather that attaches the pad to the headphone rim. Its sticks a bit too well to the pleather rim, FYI.
Give it a try! Its not uncomfortable as one might imagine once it molds/seals to the shape of your head. I took the tape off at one point and was instantly reminded why I put it on in the first place.
ps. To stay true to this thread about adding a subwoofer....I recommend attaching a real horse to your car to increase its horsepower... Is that a good analogy? hmm