Just got my M-Audio Q40 headphones today and WOW. Totally love it.
After reading through all the threads about the Q40 cable, I thought about how I could substitute the cable without spending a fortune. Turns out that Amazon has some nice cables that I could modify to fit into the Q40's threaded headphone jack. I got a Aurum 3.5mm male to male nylon braided 6' cable for $9.
It has a rubbery jack housing that you could cut with a razor blade to fit deeper into the headphone. I can still threaded it in through jack housing rubbery compression.
It fits tight and is a perfect fit. The cable is nice and not too long. I highly recommend this economical option to wonderful headphone.