The KSC 75 would be good for the rock and ska, but as mentioned, the sibilance at the high end of the audible spectrum may turn you off on them when listening to Classical Music.
The PX100 on the other hand, will work pretty much just as well for Rock and Ska and will work better with its SS on Classical and Jazz when compared to the KSC 75.
I can't say with the AKG K81 as I have yet to actually try a pair.
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