How to bi-amp with 2 two-channel amps?

You can do it either way but here is my suggestion and the reasoning behind it.
Use one amp on each speaker. One channel drives the highs(and/or mids) and the other drives the lower end. The reason I feel that doing this is better has to do with the power supply only having to supply higher current to one channel of each amp. It allows the amp to work easier. One channel isn't drawing much from the supply(highs) so the other side can use the extra draw. It allows the amp to drive the lower side a little better(generally cleaner).
The one caveat is both channels need to be reasonably close in input sensitivity to allow your speakers to remain balanced in the frequecy spectrum.
You can use "Y" connectors at each amp or simply solder a wire across the hot leads on the inputs of the amp from left channel to right channel.
Y connectors will degrade your incoming signal a touch.

Horizontal bi-amping allows you to use two different types of amps ( i.e. tubes for highs, SS for bass) you can also use two identical amps. When horizontal is choosen you will use one amp for right and left channel upper and the second amp for right and left channel lower. Note when using two different amps that the gain be the same or an imbalance will occur.Vertical bi-amping uses two of the same type of amps being eiter SS or Tubes. When using vertical bi-amp each one of the amps are dedicated to each speaker, for instace, the left channel of each amp connects to the lows and the right channel connects to the highs.If your preamp doesn't have dual pre outs then you must use a Y connector or spliter. There are a few companies that sell the adaptors.

My suggestion (based on experience) is if you have two identical amps then run one amp to each speaker. IMO, this implementation is sonically superior to using one amp for highs and one amp for the lows. YMMV.

Krell recommends one amp per speaker. Their are good arguments for both ways. I would personally experiment. Since I have two different amps, I have no choice.

By the way, "Distortion":
Bridging is totally different than vertical biamping (one amp per speaker, and your original recommendation is called horizontal biamping.

Richard

Did I get it backwards?

Vertical is two(2) two-channel amps playing independently the high and low of each speaker. One amp dedicated to the left and one right. Essentially seperated "horizontally."

Horizontal is one amp playing the L/R lows and the other playing the highs. Essentially seperated "vertically."

And, bridged would sum the output of each amp, essentially monoblocks with a single output, bi-wired if you want.

Whew.....

Now that I read that again, it sounds right. I stand corrected. Although, I knew/know better I'll probably get them screwed up again.

Sorry Overhang, awww well, If you have the cables and the time I would check out every possible wiring.