I do this, too, and it works great. I have thought about how to use a single cable and there are some options, such as stereo snake cable, but it would have to be star quad, such as this:
http://www.canare.com/ProductItemDisplay.aspx?productItemID=55, which I hate working with because I hate braided shields. But that's because I'm lazy. The only potential issue with this solution is the fact that the conductors are pretty small gauge, so the headphone send might suffer a bit. Of course, with star quad, you can double it up. Hm. Might have to try it. Anyone else interested? If I do one, I might as well do a few. It wouldn't be before August, but I've been thinking of doing this for a while.
Another one that I've thought of is tube mic cable, which comes in a number of different configurations. The benefit here is that some of the conductors, which carry voltage to the microphone, are quite beefy, and would be better for the headphones, or even for the voltage to the bass. Plus, the signal conductors would then be separately shielded from the headphone signal. Redco carries a few options:
http://www.redco.com/Bulk-Tube-Mic-Cable/.
It would be very cool if it could be obtained with 4 of the conductors at a larger gauge.
So, that's two options.
