It's your brain. Spend a week listening only to your balanced earphone and when you go back to the bass-heavy one it'll sound overly bassy again - maybe not as much as before, because your expectations have changed, but more so than now.
This is one of the reasons headphone/audio comparisons from memory tend to be unreliable, and also one of the potential contributing factors to "burn-in".
Yes on both counts. The SD-2 and SD-3 are currently over at InnerFidelity being measured and reviews will be published once I get them back.
Just FYI, there is a partial (and very optimistic...) list of upcoming reviews on the front page of this thread:
oh, you got the HSA BA100 too? some impressions?