I got the coax mod from another, very different Audio Technica set, the AD700. Some people love the feel of the AD700s on the head, I thought they were poor comfort-wise. So I did the coax mod and the hairband mod.
See this thread: http://www.head-fi.org/t/505053/audio-technica-ath-ad700-fit-and-comfort-mod
This helped, but ultimately I sold the AD700s. When I got the M50Ss, I found them pretty okay comfort-wise, but saw that the coax mod would be possible. So I experimented a little. 9.5 inches (24.1 cm) is PERFECT for the M50s. The two ends of the cable meet inside the cups perfectly without need of any tape or anything. I didn't use the foam either. I like the feel and the sound.
I tried photographing the insides of the cups, but when you have black pads, black coax, and black driver pads, it's pretty tough to get a pic that would illustrate anything. If I had used white coax it would be easier to see. Anyway, hopefully that helps.
I also tried the "sock mod" for a few days on the M50Ss but removed it, Here's the sock mod on a pair of 840s (it's pretty much identical for the M50s): http://www.head-fi.org/t/470304/shure-srh840-earpad-mod