Quote: Rockbox isn't working with an iPod Classic, so that option is ruled out. Hardware fault? Hmm, I'd say 'contact' or 'no contact' as far as hardware goes, minus 20dB makes me think M A Y B E a software solution is possible.

Hi!   I drive a Beyerdynamic DT990 (250 Ohms) through a portable head amp from my iPod Classic with LOD cable. A couple of days ago, the left channel line output dropped dramatically.  - tried several LOD cables, all the same problem, rules out faulty cable - tried cleaning dock...

I recently built an Objective2 (a.k.a. O2) head amp. Sold as kits and completely built. It has a very low output impedance and enough oumph to drive your cans. I suggest you give it a try, it won't disappoint you.