Okay, so here is what I don't understand about the glued pads: it is clearly a process change (probably because the pads do not always stay in for some...my stay on fine). In the case of this or any other minor change, they don't have to tell any customer or any of us here in this forum, as long as their form, fit, and function remain the same. There are always parts and process revisions that occur over time. Just the nature of manufacturing. The glued pads clearly meet specifications. So, with the glued pad, why is anyone taking them off NOW? If the sound quality is fine, if the external cosmetics look good, if the pads themselves are fine, then leave them on until you actually have to replace them. Then order the new pads, take off the old ones, and if you tear the old ones then so be it. You got the replacement pads ready to snap in. I say worry about it in a couple of years, or five, or never (I treat mine like gold and don't see any reason I will be needing replacement pads any time soon).
As for the bass, I had the HD598s, the X2s have the depth and slam that those fine headphones are missing. The only type of music where using the 598s may not matter is classical (and not the closed mike type). However, I do acknowledge the HD598s, especially the black SEs are lighter, more compact, and exhibit very nice workmaship. They also come with extra cables. Really a nice package... just wish they had more emphasis on their bass.