sorry for my poor english
I just wonder if you see this post?
It seem adding a impedence adapter (as u mention before, UE's impedence adapter) will fix the bass roll-off issues with the D2.
As you mention that impedance mismatching will result less bass response than the original design, or high frequency noise.
D2 have higher output impedance and get bass roll-off.
However, in their case, add a impedence adapter will end up with less bass rolled-off, and the background hiss disappears.
Moreover, in this post http://www.head-fi.org/t/544478/ultimate-ears-ue-x-pro-custom-appreciation-review-discussion-thread/45 (post #54 )
UE try to fix the impedance mismatching with a impedance adapter.
(They had claimed that UERM's attenuator is different from TF's.)
May you give me a detail review, thanks.
Edited by Yazi - 5/22/12 at 2:47am