Back again...finally got to do a good wired comparison between the two. I'll put it this way; both are top-notch in every way, however they're night and day different in terms of approach and intended sound. This is going to come from the point of view/ears of a guy who's been around live music and plays in a band for fun.
HA-2SE: Bigger, warmer, wider, thicker...less detailed and not as "3D". Bass boost is more noticeable, although it's not as "punchy". Makes me feel as if the music sounds like it is coming from a club/concert hall/venue and just sort of has that "real" type of quality to it...sometimes you guys can forget that music and sound itself are imperfect, and that imperfection is sometimes needed for musicality. It's not always about revealing everything possible at all times.
XDSD: Narrower, colder/balanced tonal range, huge clarity, tons of detail, punchy with a very "3D" feel to everything, very very very subtle bass boost, and a much more "audiophile and hifi" type of presentation that's really something else. It makes me feel as if I'm listening to a pristine recording with every little nuance being audible...it's incredible, but it also feels just a tiny bit artificial and "too clean" to me. It doesn't have a "live" quality or feel, definitely more analytical but in such a good way.
It's tough, very tough to say which is better...XDSD definitely wins in terms of resolution/detail/clarity/being high fidelity, you hear so much more popping up at you with the XDSD. However, the HA-2SE has such a lifelike character to it that is much more realistic and forgiving overall.
I would describe it as this: If you want to feel as if you are listening to live music in an organic setting, consider the HA-2SE. If you want to get the utmost experience of listening to recorded audio that sounds like recorded tracks should, with every little detail and nuance being there, then grab the XDSD.
In short, I wanna say the XDSD is "better"...but not necessarily the best choice. Really tough.