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

vertical bi-amping optimizes stereo separation and will provide an outstanding 3 dimensional soundstage.
if you like lound music,horizontal bi-amping is more optimal bec. distortion crosstalk bet. low/mid and high frequency channels can no longer occur.However, stereo separation maybe reduced.the best configuration for you depends on your listening habits and eqpt.

You could try both but I would think vertical bi-amp will be better in your case. Vertical also lets you get away with shorter speaker cables which can save some money.

Dave

Think about your speakers and your listening preferences.

With identical amps you can do it either way.

I bi-amp ESL Hybrids and the best way for me is horizontal. That way I have better control over the separation between bass and mid/high. If you horizontally bi-amp you also need to think about passive versus active, which is a whole other discussion.

Experiment and listen - always the best way to make decisions, anything else is somebody's opinion and only yours really counts.