The ksa5 is voltage limited, so for things like the he6, not enough oomph. And its single ended, although nothing prevents you from stacking 2 of them for balanced in which case its going to have serious amounts of power.
ss dynahi is for all practical purposes way overkill for all modern in production headphones. Very nice on vintage electrovoice and jbl horn speakers. I did just pick up a pair of original "voice of the theater" set, if I bring them home i'm dead for sure.
ss dynalo is what I listen to when I listen to dynamic headphones. as I only use the he6 now for testing.
any of the audio-gd headphone amplifiers are better than that eddie current piece of crap in every single way, sound quality, build quality etc. And less than half the price.
I hope the black widow is reliable because its stuffed with obsolete parts (although the layout for the thatcorp/Motorola front end is obviously there), repairing the thing is almost as bad as trying to repair a cavalli piece of trash.
compare the picture above with this for $520
http://www.audio-gd.com/Pro/Headphoneamp/NFB1AMP/NFB1AMP9.JPG