Just a quick recap regarding that half an hour listen/comparison which was intended to be with HA-S500s, but turned out to be more with my modified HA-M750s. Compared to 500 is 770 after one and half an hour bassy, with far less treble, midbass hump and general muddiness in the lower reaches.
Just like HA-M750s in stock form - but precision in treble for which CNTs are famous for menages to come trough. Soundstage is - want a better term - mono-ish, something predominantely classical/acoustical music listener as myself would put on his/hers wish list as the last thing thing he or she might wish for. A/B ing against my modified 750s brought a sigh of relief - they are no mono muddy bassy waters, but present everything in much more natural acoustics than say 500s.
They are far from the last possible stage in modding, but something reasonably dedicated head-fier may be able to repeat - and that is kind of good enough vs 500s. Not that terribly good with words, but 500s remind me of some very good mini monitors that have bass that does punch above their size, whereas modified 750/770s remind me of full size full range high quality floorstanders - it more resembles the real thing, not a ( good) scale model.
Stock 770s vibrate in the bass regions crazy enough to give me unwanted ear massage again - the whole lower spectrum, where most fundamentals of music lie, is a mess. Like indicated earlier, resonances in earcups are responsible. After taking the initial measurements, I will burn in them for 48 hours and repeat measurements and do some listening.Then, one week of complete pause to check for the longeivity of burn in effects. Everything backed by measurements.
After that I will go through entire range with Sinegen generator spaced at the closest possible intervals to see where these resonances occur exactly - and proceed from there on.
One might ask why i did not mention midrange at all - the reason is that if any audio device has bass/midbass so compromised as stock 770s, these do color sound far, far higher up, messing with the midrange; with all that bloat down there, it is next to impossible talking about midrange quality. One thing is for sure - midrange is not recessed.
Treble? After an hour and a half playtime, with CNTs - are you kidding? Much too early to say anything conclusive on this front.