We recommend only using the length of wire that is on each amp. That gives you about an 18" umbilical that will allow you to move the amp around behind the woofers quite a bit.
Keeping them short is probably good practice in any circuit. That being said, if you need a bit of extra length, I think there is some flexibility here.... look at how long the signal path gets in say a 6-stack of the 12's. It's a long run up to that top woofer !
I've actually got some excess length from the wiring on my A370's that I'm going to shorten up.
I was pondering that. Even a triple stack adds at least 3 feet to the existing amp leads.
Another question, should the speakers (coil drivers) be paralleled in a "star-ground-like" configuration where all 3 pairs of wires are the same length or just "daisy-chained-like" where the 1st driver is electrically closest to the amp and the 3rd driver is the electrically furthest from the amp.
I know when I run low voltage lights in a daisy chained fashion, the light closest to the PS is the brightest and the one on the end of the chain is the dimmest so I usually try to splice in the PS supply line into the middle of the light strand (T instead of a L to average out the brightness levels) which causes there to be 2 brightest and 2 dimmest (brightest in the center of the yard and progressively dimmer as they progress to the left and right sides of the yard).