Two Sunfire Signature's wired together?

I've used two Sunfire Signatures bi-amped with two different sets of speakers and the results were very different for each set of speakers.

I first used a pair of Sunfire Signatures to bi-amp a pair of Infinity Kappa 9....very inefficient notorious hard-to-drive power hogs. Bi-amping the Kappa 9 were a world apart from using a single Sunfire Signature amp. The improvements were dramatic.

I then bi-amped a pair of Infinity Rennaisance 90 speakers.
It was a complete waste of an extra amp. Bi-amping was indistiguishable from using a single amp with these speakers. They are much more efficient than the Kappa 9.

Regarding my post above:

I used a vertical bi-amp configuration in my setup. One amp per speaker.