xlr splitter?

Try it...those adaptors Tim linked you to are cheap enough to give it a shot. Technically, you will not get the best overall scenario. But, it depends what you want to do ultimately. SEE WHAT IT SOUNDS LIKE.

if you want to control components and pigtail length, you can have one built at Redco

I think my neutrik/mogami set costs about $15 ea.

I am biamping with balanced interconnects but my amps have a switch on the back so only one cable is needed. If I switch amps and continue biamping I will construct my own cables. An easy task if you have any ability.

I don't think you'll find a 4-way xlr y-adapter available off-the-shelf. You could combine three 2-way adapters to provide a 4-way split, and there are several of those available at B&H Photo Video. Here is one.

However, keep in mind that the preamp will see a load impedance equal to the power amp's input impedance divided by four. That may produce degraded deep bass response if the preamp has a coupling capacitor at its output (such as tube preamps typically have), and/or an uneven frequency response generally, if the preamp's output impedance is higher than a small fraction of that reduced load impedance.

Regards,
-- Al

Upon re-reading your question after submitting my previous response, I think you are saying that you only need a 2-way split, one 2-way split for each preamp output channel (left and right). In which case you can use any of the 2-way adapters that have been suggested, including the one I suggested which is available at B&H. And of course the load impedance seen by the preamp will be the power amp's input impedance divided by 2, not by 4.

Regards,
-- Al