So it really helps to know the configuration of your amps. Are they:
- True monoblocks: no switch to stereo mode, and cannot be used for vertical or horizontal bi-amp until you have 4 of them.
- Stereo amps with a switch to PARALLEL the L/R sides for mono operation: sometimes tube stereo amps offer this option, yielding up to TWICE the rated power output - like my VAC Signature 200iQ. In that case (200iQ), using a pair of amps in mono mode yields a HUGE performance gain over using a single amp in stereo mode. This is more of a performance gain than you’d get via bi-amping, IME.
- Stereo amps with a switch to BRIDGE (series?) the L/R sides for mono mode. Many SS amps offer this option and advertise up to FOUR times the power rating! There are a few downsides: you lose headroom for driving tough (low impedance loads). There is added circuitry for signal inversion (in worst case an opamp) that will negatively impact sound quality. In my experience, bridging sounds BAD. Worse than a single amp in stereo mode, unless you’re REALLY starving for power. Not recommended. In this case, you’d for sure be better off bi-amping with dual stereo amps, in either a vertical or horizontal configuration.
In my experience there can be some modest performance gains to bi-amping, but "proper" monoblocking is usually best. Also if you want to bi-amp, I'd recommend sticking to two IDENTICAL stereo amps or four identical mono amps. Mixing amps (even different versions of the same amp) gets real messy.