Passive Bi-Amp using XLR-Y Adapters - Amp or Preamp?

I want to use two power amps for my speakers [passive bi-amping].One of the amps will power the left and right posts on my loudspeakers, and the other will power the left and right midrange/treble posts on my loudspeakers.
Since my preamp only has one pair[left and right], I will have to purchase XLR Y-adapters to make a pair of outputs per channel.
My question is:
For the least sonic compromise and the least signal degradation, would it be best to buy XLR Y-adapters that split the signal at the preamp or at the power amplifier?
Thanks in advance.
Use one amp for left speaker and the other amp for the right speaker. Use the splitter at the amp ends. Place each amp near the speaker it will drive with short speaker cables of your choice.

Buy the way, Cobalt Cables has a one day only 30% off sale on XLR Y-splitter tomorrow.

i believe the cobalt sale is today so hurry it ends at midnight.

aloha keith
purist has some very high quality xlr y adpaters.

good luck,