More Power???

NO and NO. Series: the output from the first amp would likely overload the inputs of the second and the power is not additive. Parallel: any slight output impedance difference between the amps may cause one amp to see the other instead of the speakers. I suggest you do not even consider trying either. Do a forum search on bi-amping and dual-mono for responsible and safer alternatives.

Assuming we are dealing with identical amps, would it not be better to bridge each into a mono amp? In such a case the power would be more than doubled. Someone more technically astute than me could explain why and how much power would then, at least theoretically, be available. I am not certain bridging is always feasible though. Sounds like what you are attempting is more like bi-amping, which can be done with a number of speakers; again this requires two identical amps and speakers that can be bi-amped (the crossover actually being in two sections that can be disconnected). Again someone with a better technical background than mine would be called for.

Bridging a stereo amp into a mono is not without compromise: damping factor typically degrades by half, which decreases bass articulation & control, perhaps even masking HF subtleties & nuances to boot. But other than bridging, there is no other method of achieving the aforementioned at least that I'm aware of.