I actually liked the 325 with the big bowls on them the best, but I also realize I have a pretty intense bias in terms of comfort. I could barely listen to the 325 with the flat pads because the weight of them drove them straight into my ears in a painful way...I couldn't tell you how they sound because I could barely listen to them.
Having recently taken a DEEP headfirst dive into all things Grado (I'm on vacation, it's keeping me out of trouble...) I know the answer to this.
1) there have been a few guys that tried it...and one company actually made an adapter if I recall...basically the solution is a sort of ring/frame
thing that you use to attach the pads to the phones. I don't recall what they said about the sound, it seemed like too far to go...it changed the character of the headphones too much for my taste. It's a simple formula, I didn't like the idea of adding complexity.
2) those Beautiful audio pads look amazing...and EXPENSIVE, relative to what you can get Grados for (I got my SR80e used for $50...I can get a new 325e for less than $200.
In terms of pad rolling, the Grados are limited to: stock pads (or replicas of them) and the two options I just mentioned. (Plus some people did the ole sock mod...but...naw.)
you kind of just have to figure out which pads you can tolerate the best....but my most important point is
3)
@Slater do yourself a favor and get some Grados. They are really fun to take apart and play with...really well designed in some ways and kind of crappy in other ways....but they sound awesome, a great bargain headphone with tons of tuning potential. It's worth the money just to get a set, take them apart, tune them a little and really get a feel for what Grados are about. Even if you decide they aren't for you and you give them away as a gift, it would be worth it.