Hi pjyi, thanks for asking!
Just tested for you:
The Brainwavz HM5 earpads perform surprisingly well on ATH-R70x! It is bigger and more comfortable
The HM5 earpads are oval, and R70x frame is circle, so need some stretching to fix them to R70x. But still doable.
The sound signature is shifted to the treble side, overall tonality is brighter than the original stock earpads. Not much brighter, just nice, still within natural sounding category. If someone needs treble boost on R70x, the HM5 earpads does it naturally in a nice way.
Bass is slightly leaner, but still pretty good, and also less warm. Overall is pretty good, another nice variation of sound signature we can get from R70x
Personally I still prefer the sound signature of the stock earpads, but HM5 signature is interestingly pretty good as well, and it is more comfortable for people with larger ears.
FYI, my review on Brainwavz HM5 Earpads:
http://www.head-fi.org/products/brainwavz-hm5-velor-memory-foam-replacements-earpads-suitable-for-many-other-branded-large-over-the-ear-headphones-akg-hifiman-ath-philips-fostex/reviews/12533