Anyone prefer horizontal bi-amping their monos?

What do you mean?
Two monos per side into biwired speakers?

or is a mono a speaker?

I think many people run a mono for each speaker.
If nothing else you end up getting a short speaker cable.

And I suppose save some rack space if one can hid them behind the speaker.
And also those cable lifters go out the door when the speaker cable is going vertical.

You sure got me a scratchin’ my head with your question.

The question is also stretching my imagination yoga style.

Do you mean running both woofers off of one mono amp and the higher bi wire terminals off the other amp?

You are going to need a sketch from the 2 RCAs (L/R) from the preamp.
L (left) goes to the left hand side speaker.
R goes right.

If they are stereo amps, I would vertically bi amp them personally.

@re-lar-kvothe thanks for sharing the diagram. Clears up any confusion.

"A picture is worth a thousand words"

No so fast… that is two stereo amps.
The OP has 4 mono amps, so some mention needs to take place that the amps are split down the middle into two parts.

And a further mention of what the active cross over is, and how it works.