I ordered the black B4-X upgraded dual mono version with balanced output a few days ago to try with my HE-4XX and, when they finally arrive, my Tin Audio T3 in balanced mode. It hasn't shipped yet but they estimate I should receive it sometime between March 21 and April 11.
I can't say I appreciate the aspect of having to wait the better part of a month for it to arrive but it didn't look like there was any faster option. Anyway, there's plenty of things to keep me busy until then.
When everything finally arrives I'll let you guys know how it all sounds since there seems to be very little info about the B4-X model.