If you want to run the K7XX balanced then you will need to change the 3 pin mini-XLR jack in the headphone to a 4 pin, and do a little re-wiring between the left and right drivers.
I built a Mogami cable and there is no difference in sound from the stock, I just wanted a shorter cable. The topic of headphone cables making a difference is a touchy subject with many, I'm on the side that says there is no difference between cables unless the original is defective or of very poor quality. FWIW I've had high priced cables from Double Helix and Forza, beautifully crafted and a joy to use but there was no difference is the sound compared to the Mogami, Canare and Cardas cables that I've built. If looking for a "huge difference" the only way is to get another headphone.
As for the ear pads, I still have the originals with my K7XX. I've done some pad rolling with my HE-560/400i/400 and also with some Grados and Beyers, for the most part changing ear pads will usually affect the entire spectrum of sound so while one aspect might get better you might lose something with another aspect, YMMV.