Instead of blowing stuff up, where can I find...........

[hamerhead]

.... small (dimensionally) power amps that I could stick inside each sub cab?

I'm going to test them with a Crate Power Block just to see what happens, but having built-in amps would be way cooler.

[Bloozguy]

There is a website called classdaudio.com that sells power amplifier modules and kits. I don't know how much power you're after, but they have at least one that delivers 600 watts bridged. Other than what I've seen on their website I don't know anything about them. You might want to contact JohnnyB for expert guidance.

[JohnnyB]

These days they most often take the form of "plate amplifiers," which have the amp, crossover, and connections all mounted to one plate that becomes part of the sub's back panel. Here are sixteen of them ranging from 25 to 1,000 watts from PartsExpress.

This video may help a bit too, and YouTube has

(check the column on the right):

There is also a category of Class T palm-sized amplifiers, but these are more for general purpose use for desktop or other compact systems. They're usually 10-25 watts and the most powerful one PartsExpress offers is 50 watts.

If you're going to self-power a sub, in addition to an amp that fits inside, you need heat sinking to the outside, adjustable level and crossover controls, a power supply for AC, and RCA and/or padded (speaker level to line level) speaker terminals to accept line level signal. Some also have an EQ boost at low bass (e.g., 35 Hz) to flatten out the bass curve for a large woofer in a small box. The plate amp provides all of those in one package. The challenge would be routing a rectangular hole in the sub cabinet to accept the plate amp. If you're proficient at that, then this should be an easier project.

You could also do it with an external amplifier, but you'll still need an adjustable crossover or low pass crossover. If you got a mono amp (like a used QSC from a pawnshop) with volume control, you could match levels without an additional preamp but you'd still need some sort of crossover to send just bass signal to the sub.

[burningyen]

Check out the Matrix GM50.