Channel imbalance will just push the soundstage over to one side, or, when it varies with frequency, cause instruments to wander around as they play different pitches. The Havi's 4-wire cord is designed to
reduce crosstalk by keeping the signal returns separate. Cross-fading does make the soundstage appear wider, but to do that you need to mix in some of the other channel
out of phase, which is the opposite of crosstalk.
My best guess is that the Havi's excellent soundstage may be related to some sort of
Haas effect produced by the serial-wired drivers at different distances from the ear canal, though any timing discrepancies will be very very small.