According to my analysis, any biwire improvement is due to the returns being separated, so it might make sense to leave the jumper on the High terminals only. That is oposite to what you describe. (I assume that the crossover is implemented on the High side of the drivers. It could be done the other way around).
If you want to investigate further, try long runs of #18 speaker wires, and you might hear something.
If you want to investigate further, try long runs of #18 speaker wires, and you might hear something.