As I have the idsd Dac for a few day now, I have ran some test, and beeing who I am, a lot of tests were about metal ^^
Right now I'm listening to the whole Winter's Gate from Insomnium.
I know the TH900MK2 from Fostex is not perfect, but it sure pack some good things metal wise, at least, with the dac/amp.
the first track of Winter's Gate (if I dare say so, as winter's gate IS one track ^^) is incredibly fast paced, double bass extensive, two guitars replying to each others, and all that is very defined, very well place stage wise. And, that's the most importante for me in metal listening, drum beat, bass, are not blurry. Easy to read, powerfull, impactfull. I'm going to test the same track with the Audeze LCD GX (a so called gaming headphone, but a jack of all trade).