The adapter they come with is a little better than most generics, as far as how well it is built, but performance should be the same. Its a semi-universal screw-on adapter that works with several other brands that use screw-on adapters such as AKG so you can probably find one if you look around. But if the easiest solution is a generic, go for it. Sound quality should be the same.
FYI, I found a screw-on adapter on Amazon that looks identical to the ones that came with my Beyers and K712. Its a little pricey though. Look around for something like this if you want one that will screw on all the way:
Also on ebay for the same price but without the supersaver/prime free shipping minimum:
Edited by devhen - 1/16/14 at 5:00am