I hadn't heard those terms either until recently in another thread. Horizontal bi-amping is when you use one stereo amplifier for the low frequencies and another amplifier for the highs. The advantage is that you could select a high power amplifier for the bass and use a smaller and likely better quality amplifier for the highs. The vertical option is when you use one stereo amplifier per channel with one side for the bass and the other for the highs.I've never heard those terms before, what do they mean please?
Bi-amping vs Bi-wiring
Likely not very common unless you look at professional equipment as well. They are very common in the car audio world. You can find many deals on eBay. Some units designed for domestic use are greatly overpriced. If you go the DIY route there are many boards and kits available for very little money.Where would one purchase an active crossover? That is correctly tailored to the speakers in use? I've never seen such a thing advertised within the domestic hifi scene.
The only real advantage that I can see for "passive" bi-amping is reduced power dissipation by the power amplifiers.