Are the drivers of the amperior and hd25 exactly the same? If so, the $150 premium for an aluminium cup is a bit steep. $50 maybe. Also, does anyone knoe if the HD25-SP uses the same driver?

The amp seems to help the freq response to even out. ie, adds bass to an otherwise vacant curve.

Any pics of the mod?

I have to agree. I demoed the UR55s a couple months ago and fell in love with them. I wouldn't say they are the most articulate or transparent cans in the world, but they do exactly what I like. The bass is full, deep and tight, but not bloated or overdone. The mids are clear but not harsh at...