Hmm, perhaps jfunk can write a followup for us regarding the pads on these two headphones. I have tried using some different pads with my Amperior for aesthetic customization purposes, but I have found that they changed the sound so dramatically that it was not worth it. I used some Zomo aftermarket pads and they made the Amperior sound so bright and sibilant that it hurt my ears, while old HD25 pleather pads made the bass super-boomy and also not pleasant at all. The point I am trying to make is that pad-rolling makes a huge difference with the Amperior and I am really curious what using the Alu pads would sound like. I did not find the Amperior to lack in technicalities and the 'blurry' quality of sound that you describe seems to me like it could be caused by the velour, which indeed does oftentimes make things sound a bit 'blurry' in comparison to well-sealing pleather or leather.
If the Alu really does sound better than the Amperior while being cheaper, I will have a bone to pick with Sennheiser :) I'd want them to replace my Amperior with an Alu for free!