I'll throw my 2 cents in. I currently have a pair of Mirage OM-9 that I am running in a passive horizontal bi-amp setup and they sound absolutely fantastic this way. I tried an normal stereo setup with them and they sounded ok, but nothing special. I went to the the bi-amp setup and it was like I went out and bought new speakers, the OM-9s just came to life. IMO Mirage designed their crossovers for exactly this type of setup. The amps I was using initally were NAD 2100 now I'm using a NAD 2100 for tweeters and a NAD 216 for the drivers.
I would suggest if you have or maybe can borrow and extra amp, give the bi-amp or tri-amp a try and see what you think. If you run the amps horizontally then they dont all have to be the same amp and will give you an idea if its worth spending the extra on more amps. If you are using different brand/model amps you will have to pay attention to phase as the amps may be out of phase with each other, but that is just a simple matter of flipping the wires around till you get the best sounding combination.
I would suggest if you have or maybe can borrow and extra amp, give the bi-amp or tri-amp a try and see what you think. If you run the amps horizontally then they dont all have to be the same amp and will give you an idea if its worth spending the extra on more amps. If you are using different brand/model amps you will have to pay attention to phase as the amps may be out of phase with each other, but that is just a simple matter of flipping the wires around till you get the best sounding combination.