Bi Amping: highs and lows or a seperate amp for the left and right.

Why would I bridge? And what, the amps? if bridging amps, would need 4 stereo amps then instead of 2. 

The amp is currently driving the speakers without issues, i don't think the impedance changes when splitting low/high? Just that the low will have the low impedance (typically), and the high not anymore. Vertical: one side of the amp low impedance, other side high. Horizontal: one amp only high impedance, the other only low on both channels. 

Distribution of power is determined by arranging vertical vs horizontal. In one setup the stereo amp running the highs sees very low power demand, stereo amp running the lows sees LOTS of power demand. Vs. summetrical (per amp) running 1 amp for one speaker, high channel low power, low channel high power. 

"Plus, you can run the tweeters or mids/tweeters from a channel that doesn’t have the burden of driving heavier woofers, which has some benefit too." Not in vertical. There, the amp's ONE channel is burdened, and typical stereo amps share power supply. THAT would be (to me) the only reason to run HORIZONTAL, keep the heavy lifting in one amp, and easy peasy for mid/high with the other stereo amp.

But as you stated, differences likely minor. And vertical already sees the load on each amp 'halfed', plus crosstalk/separation, etc. Would be sweet to be able to physcially place each stereo amp near the speaker to reduce long speaker wires (and run low voltage signal lines for the distance). Or?