I've thought this too. At first I was thinking..what the heck is the point of a $200 cable upgrade when you still have stock wires inside going from the metal rod to the driver.
Makes no sense but there is still audible benefits of cheap DIY single entry cable upgrades.
Strangely with my K702 and 3 cables I couldn't detect an ounce of difference until I got my HRT MSII. Wonder why? When I got my ODAC the differences were even smaller!
Sometimes I use my mini to mini Cardas cable interconnect ($35!!) with a $2 four inch Y-adapter (with copper wires inside) and it still gives me some audible benefits.
I think if someone bought a $100,000 10 foot extension cable, a Sennheiser 1/4 to 1/8 5" adapter is not going to magically degrade the sound.
And yep, you'd have to be a moron to use a $20 adapter if you buy any $100,000 cables. Ok that sounded weird. Using a $20 adapter is bad, but buying a $100,000 is perfect OK. Totally makes sense!
I'm sure I've made this clear, but the metal headband rod doesn't go straight to the drivers
The rod is soldered to some wires that go directly to the driver.
Maybe replacing these rod to driver wires with what's used for the single entry cable upgrade is a good idea too. If you can hear a difference when replacing 2" of wire you must have the best ears in the world.
I also replaced my TBSE stock cable with a $15 Mogami cable and theres still some minor improvements despite the ultra thin internal cables inside the headphone. As long as the internal wires are very short it seems OK. Don't ask me why or how!
BTW sorry about the cable crap, but very few cable upgrades for me with the Q701 have sounded better than the stock cable. Only one i've liked is the one I made with Mogami W2893. Didn't like DHC, ALO SXC, Canare or some generic Belden. Stock was almost best, but only due to preference. ALO SXC made my Q701 sound too cold and analytical. ALO SXC was nice until I used it for a week and could figure out the differences.