Hi Doug, a couple of things to try:

I've been unimpressed with the results of passive bi-amping, so don't expect much -- but it costs almost nothing to try. You may decide differently. One Outlaw amp does pretty well on its own, so there's not much more to gain adding a second without altering the speaker, in my opinion.

Without knowing more about the speakers, I would be careful with this. If the net impedance of the drivers is different between the two speakers, connecting them in parallel to a single amp channel could do more harm than good. If the RB-25 drivers are lower impedance than the RF-25, it will mean most of your power is routed to the RB-25, which probably sounds worse out of the two. Even if the drivers are the same, the internal crossovers and cabinet geometry can change the total impedance. You can also strain the amplifier if the total impedance is too low. If you go this route, test it with low signal levels and a sound meter to make sure they're closely matched before cranking it up!

Instead of this, I'd probably drive the whole RF-25 with one channel and the whole RB-25 with another, feeding the same signal to both amps. I'm assuming the sensitivity of the two speakers is similar.

Yeah, that could work. You might want to experiment further with room placement too, in case this setup gives you diffraction effects. Sounds like fun.

-RM