Lol. While this isn't the "O2 haters thread", I would patently disagree that its 'over-rated'. By who, exactly? Also, I am curious about how it is a 'bottleneck' - it has proven to be a good pair to the HE-400 over time. More than enough power.
Anyway, I am wondering if it is time to start an HE-500 lover's thread, since this one is slowly turning into a discussion of all the other headphones aside from the HE-400 that rule.
I myself have gone from pad swapping, to fine-EQing, back to flat, and currently use a 6 db boost at 50 hz (through the windows mixer) because I've been bass crazy. While its hard not to fiddle with these, I still love the spacious, detailed, and slightly aggressive sound. I will never defect! The law of diminishing returns says it can't be THAT much better at the top, and frankly the money I am saving is buying new CDs!