I know many will have a different opinion about the sound, but passive bi-amping does not provide much, if any, output increase. Certainly it does not provide the additive output of both amps which is a common misconception. Amps of "x" power provide only so much usable voltage swing before clipping. Thus, adding another amp of similar voltage swing does not increase your clipping headroom to any significant degree because both amps in a passive bi-amp setup are reproducing the voltage swing of the full range signal.
You would be much better off to sell both amps and get one amp that is more powerful, IMO, based on what you seem to be wanting.
You would be much better off to sell both amps and get one amp that is more powerful, IMO, based on what you seem to be wanting.