It was with a Yamaha YH10ms shell, which was a rebadged Ultrasone HFi450 (I think) and SFI drivers. My attempts at getting even sound out of that were mediocre. Weird peakiness all over the treble; not super piercing, but aggravating nonetheless. I can't remember how much cotton I used in there but it was a lot. The cup has the main chamber and this sort of ring area along the outer edge (aligned over the S-Logic vents on the baffle). I'm not saying it's impossible, but dealing with both the cup and S-Logic chambers is a bugger.
If you want to try an Ultrasone transplant, I'd say start with a Pro frame. Those are simpler and sturdier to work with.