Kernmac pretty much has it spot on about the sound change with the W5000 pads. The W5000 are MUCH more comfortable compared to the stock AD900 pads for me because the stock pads made my face itch very quickly. I could wear the AD900 + W5000 pads forever with no comfort problems at all. It would make your ears a little warm, but it won't get hot and sweaty or anything. Without the tissues, my ears would press against the drivers and it would start to get annoying overtime, but with the tissues, my ears have a perfect distance away from the drivers and they become extremely comfortable. It was necessary for me to get the W5000 pads for my AD900, but if the stock pads don't irritate you or anything, then you should just stick with it because those W5000 pads aren't cheap at all lol.
Ordered! Thank you for the swift reply. I'm looking forward to this 'mod'. I'd love to have an AD900 with more comfort and added bass performance. Nice!