Don't forget the K701 and Q701 also use different part numbers for the foam behind the pads.
The K702 and Q701 share the same foam pieces.
Can anyone check your foam on the Q701 and tell me what it looks like? Are they both very sparkly and rough?
I checked the foam and they appeared very similar. I don't remember if they were identical, but they were close enough that I couldn't really tell them apart and sound differences should be very minor.
I know someone tried it, but try the K702 cable on the Q701. It may require listening to an entire album and then switching back. Probably a huge placebo effect, but maybe someone with golden ears can tell the difference more easily. Even though the K702 and Q701 cables are the same thickness they could be slightly different.
Again, from my testing if there is a difference, it's extremely minor IMO. The cables sounded (and felt) identical to me.
The changes could be a combination of the button, cable and two foam pieces. There's also the internal wires going to the drivers that could be slightly different or maybe a higher gauge of wire is used. Probably unlikely and wouldn't change much.
So far, none of those things have accounted for the differences I've heard. I swapped everything except the two foam pieces behind the pads (they look close enough to me between the K702 and Q701 I couldn't really tell the foam apart between them).