Yeh I agree my first exposure to some modern Stax besides the 407, 507 was the Mk1's thanks to a mate of mine and they sounded extremely intimate. Funny enough we tried some general piano sonatas, classical beethoven stuff and few other modern pop and it sounded good with all of them I believe at the time we were using some 727's and I can't imagine how much better it would sound if he had a better dedicated stat amp as I heard that the Mk1's require some juice to get that sound just right.
Didn't like the 507's either.
I believe Audiocubes still has some headband replacements. Need to check.