@pbarach, appreciate the detailed reply, I'll try some the recordings you noted to see if my HE400i displays the same fuzziness to the piano.
Gave some tracks a listen on my old HE400i (SMC/back plate, sorbothane, grill mod, attenuation rings) the piano is rendered clearer/cleaner than my HD650 and I asked my friend who still has a HD600 and old SMC HE400i to give some tracks a listen and she also noted that her old SMC/back plate, grill mod HE400i also sounds just a touch cleaner than her HD600 and HD660S with some solo piano tracks. I guess with this informal comparison I'd have to assume that there is a larger differences between an old SMC HE400i and newer ones (reason for the price drop?) than I originally heard. I was considering selling my old HE400i since it gets little use but since it seem to perform better to me than my HD650 with some genres/tracks that I haven't really tried out much before since I normally use my HD800, HD700, T1gen1 or HE560 for classical. Also tried my HD58X and its no match for my HE400i with well recorded classical, jazz and blues but is not as engaging / fun sounding with rock, pop, Kpop, Jpop, and oldies.
When I had my HD600 I remember them being quite good for classical and jazz but with other genres like rock and pop the small peak at 3.5-5khz bothered me at times. But I still prefer my Ypsilon S1 build since its fairly close in tone to the HD600 but its better extended up and down, doesn't have the peak, and is easily driven by a phone or headphone jack of a computer.
And thanks for the music recommendations, love it.