As some of C-hing already said when using Bi Amp, both 2 pair of cable better to have same length.
I want to know how about the material. Normall it shoud be same material.
But How about if HF --> silver cable
LF --> copper cable
Any comments?
If you have knowledges about the characteristics of your Amp, Speakers and cables, it should have better result than using the same cables for HF and LF.