@jason41987
Contrary to popular belief, leather/pleather pads don't only increase bass. In my experience, I've seen them more frequently increasing treble substantially. If a headphone was designed with a velour/cloth pad in mind, leather pads will probably alter the sound A LOT. And it's not like the SHP9500 is the kind of headphone whose treble needs boosting.
Velours will probably fare better. I'd have preferred the suedes as a middle ground, but that's just from how I guess the headphones would sound with them. Or you could try hybrid pads if you want another inbetween solution.
With all that said, Luke is far from an idiot. I've seen him a lot around these forums, and he's usually very helpful and has a lot of insight. I'd listen to what he has to say and don't dismiss him because I don't like what he said. A quick search would've given you the answers you need. You don't have to read through all the countless posts in here, just search the thread and you'll find what you want 95% of the time. You have to understand that seeing the same questions pop up again and again and again and again because people can't be arsed to click on the search box and find the answer that's already there is infuriating.
Finally, the assumption that open back = wide soundstage is just plain wrong. It's more often that you encounter open headphones with wide soundstage, but that's about it. There's closed headphones with massive soundstage (Argons) and open headphones that are really narrow (HD600). It's a matter of design and frequency response. As I said in another thread, the generalized open vs closed back comparison is almost always invalid, unless you're talking about open and closed variants of the otherwise same headphone. Compare specific headphones, disregard the design principle if you don't have a reason to go with one over the other (eg closed backs for portability). The SHP9500 are not a wide headphone, sadly.
PS : Quick sidenote, and part of the answer that Luke got mad because you didn't search about it, is that you don't need the adapter rings. The pads can be stretched over the cups with a bit of effort. Using these rings with aftermarket pads deteriorates the sound.