Can I Do This?

I know some of the new power series amps from rockford, as well as some of the kicker amps, let you hook up identical amps together to drive a single output with the power of both amp's combined.  I'm sure some of the other manufacturers make them too.  But this only gives you a single output so it wouldn't help in your situation even if you had amps with this feature.

You will not be able to combine the power of all three amps, for many reasons, but the first of which is that each voice coil has to see the exact same signal and the exact same output level.  Unless the amps have digital gains (+ & - buttons as opposed to a knob) then it is technically impossible to have the exact same amount of power going to both voice coils.  Even then, you have other factors in play such as amp efficiency, damping factor, signal to noise ratio, THD, etc. that will all make it impossible to match up (or at least proportionally divide) the power of the amps.