My HP1

Slight upper mid/lower treble dip/recess veil on strings.  Good midbass, low bass, but upper bass not as pronounced, lacks a bit of punch.  Very neutral.  Warmth without congestion.  Could use much more clarity and blackground compared to the HD800.  Smooth treble, relatively decently extended for a warmer sounding phone.  Maybe not so much.  Mine feels more balanced, coherent and resolving overall (except those areas/peaks where the modded version brings our better clarity).  Mine is more neutral than the typical HP1000s out there IME, so there are less issues to fix.  Mine has more air, space and room to breathe providing a more relaxed and resolving listen.  Piano notes and chorus are more precise and articulate on Estefan’s Coming Out of the Dark.
   
Don’s HP1

Could be a bit more sensitive than mine, can’t tell if they are hair louder or just clearer but more congested.  Mine have the Grado Reference cables for whatever that’s worth.  Better upper bass punch and upper bass clarity.  More midbass sense which is present in most HP1’s compared to my own, could be reverb.  Some areas across the FR seem a tad clearer.  This adds to an overall sense of better overall dynamic contrast to the timbre of various instruments.  Strings seem more veiled and smeared a la Abyss. Maracas and the kick drum on Hotel California is more veiled and intro applause is murkier.  Too much sense of an upper mid lower treble veil muffling female vocals and other information in those registers.  Reminds me of unmodded Abyss veil but also pushed up higher to the next registers as well.  The enhanced clarity in certain parts seems to make the FR seem a touch more uneven and fatiguing for me along with the bass compression.  Imaging is bit more nebulous, seems like there is a slight reverb or echo.  Richer, more syrupy sounding. Piano and the chorus at the start of Coming out of the Dark is vaguer and the chorus more shouty and distorted.

Unlike the HD800, distortion and clarity seem to take a bigger hit as you crank the volume on the HP1/2.  HPs are a better low to medium volume phone for sure IMHO.