Bridged amps vs stereo vs monoblocks.

As I understand it when you bridge an amp you will double its output at 8 and 4 ohms, but not 2 ohms. 

That is not always the case - it depends on the amp. If you have one with a sufficient power section it will 'double down'

I own a pair of amps that put out 40 W into 8 ohms stereo, and 230 W into 1 ohm. I run them in bridged mode and they put out 160 W into 8 ohms and 500 into 1 ohm loads.  I am not using them with speakers that require that but when I bought them they were happily driving one of the harder speakers, a pair od Apogee Scintillas in 1 ohm setting.  The poster would have to research the amps he is considering to know whether they will be happy with a particular load.

You are correct, though, in thinking that it isn't always a strict doubling of power. My bridged amps put out 160 - 280- 400 - 500 W into 8 - 4 - 2 - and 1 ohm loads.

Personally I like a really good stereo amp or monos.   Buy a more powerful amp on the first place.  

I used to do the horizontal bi-amp with an affordable, more powerful amp driving the bass and a quality Krell integrated driving the top with ok results, but I finally broke down and bought a pair of Mc611 monoblocks with a dedicated pre/dac and can appreciate the difference. I would do what I was comfortable spending which probably cost me more than had I just done it right the first time,  oh well.