BiWire Jumpers on biwireable speakers.

[Jean-Marie]

Why not just follow manufacturer instructions?... There is nothing to loose.
Speaker internal cables (for bass and treble) may have length adjusted in conformity with jumpers cable type and length.

The claim is on Audioquest's web site, not a speaker manufacturer's. You're right, there is nothing to lose. Nothing to win either.

Internal speaker wires are the length they need to be to reach the drivers. I've never heard of a designer making all wires a different or the same length for any purpose. Probably because they know it's a waste of time.

Cable length needs to be put in perspective especially from a time perspective.

I'm currently using 5m on the left and 2m on the right, so that's a 3m difference.
At the speed of light (3E8 m/s) that's a huge difference of 10ns!
given the speed of sound (340 m/s) that's 3.4µm!

I'm not that precise with my sitting, nor my neck stiffness...

This to say that the length difference with cross overs will be 2 orders of magnitude lower, meaning that if you could hear a difference, then you should better glue yourself in a block of concrete, because any movement greater than 30nm would have a greater impact than the difference if lengths of cables....

Jean-Marie