I'm still using the original pads, so perhaps it would be worth trying out the MSR7 mod.
Sub bass is subjective, no pun intended. I tend to go by tested levels. I have specific tracks, one in particular called "Weekend" by Kelis, (where about one minute into that, and at various other times, she does this break where she says "boom boom" along with an 808 low tom sub bass boom. The first round are audible in most headphones as the energy is in the 30-40 hz region. The lower note that kicks in later will really reveal sub bass quality. I have it in my iPhone with other test tracks (that highlight bass, mids, treble, or staging, to evaluate headphones, and an iPhone 5S DAC is one of the best in cell phones). Both the ATH-M50X and Sony MDR-1A stock pass this test brilliantly. The highs are too aggressive on the ATH-M50X, causing the mids to seem recessed. As stock they are uncomfortable, and almost every pad swap reduces bass and increases treble. The Sony MDR-1A has less aggression in the highs, but has some higher mids that could be troubling. The ATH-MSR7 ear pads make them fit much better, and it seems they increase treble detail, do little to the high mids, and reduce the mid bass while keeping most of the sub bass. So the sound is a little colder, but more detailed and spacious.
The Meze 99 pads ($20, direct from their site) are the best. Like others, they wrap around the outside of the cup, you can't click them in place. They fit very tight on the cup, take your time putting them on and then also make sure you push in any area the inner plastic ring on the pads project beyond the foam, so they are properly aligned. You'll understand when putting them on. At first they are firmer than stock, but soften up nicely with body heat and use. They're more spacious and comfort is great with time. The treble is more detailed and spacious, that high mid peak is mostly reduced and the true mids (500 hz to 2 khz) are slightly elevated to where they should be, making them warmer. They'll also keep the mid bass, which some find bloated in stock, but they offset that by increasing their low sub bass levels. As a result you can listen more quietly since the mids don't vanish and the treble and low bass have enough energy so you don't lose those when listening quietly. Light weight - comfort, they excel for long term low level listening while I'm mixing, as an alternative to the studio monitors and custom subwoofer that I prefer to mix on. This will help preserve your hearing, whether mixing or just listening.
