Gofast...Regarding polarity: just do both channels the same. If you worry about "absolute" polarity connect the inphase signal amp to the Red speaker post.
Although you may want to experiment, Plato's comment is worth consideration. One of the benefits of bridging a stereo amp is that the draw on the power supply is more even, because one amp draws positive voltage while the other draws negative. Many amps will deliver more power when the two channels are driven out of phase. With two Mono amps this does not apply.
Although you may want to experiment, Plato's comment is worth consideration. One of the benefits of bridging a stereo amp is that the draw on the power supply is more even, because one amp draws positive voltage while the other draws negative. Many amps will deliver more power when the two channels are driven out of phase. With two Mono amps this does not apply.