Well...the laws of thermodynamics - especially in relation to conduction and convection - won't change the overall heat-sink temperature and create one side hotter than the other...

Fans could help, but it'll be tacky and noisy.

You've said the channels are bridged. Is the final impedance on the subwoofer channel 2/4/8 ohms? Is/are the subwoofer(s) DVC? Can they be rewired to a HIGHER impedance? If so, try that, and re-adjust the gains (up).

I can elaborate more about why this will lower overall temperature and not have a significant change in power/output if you like...

Gotta go for now...

 

what laws of thermodynamics relate to heat flow.

i think you would be talking about heat transfer. the law of thermodynamics don't relate to individual components they talk about how systems use energy. An 90% of the stuff used in heat transfer talks about ideal scenarios and doesn't take into account which way the air is moving, heat soak etc...

how would the higher impedance lower temperature and not drop the output. if you raise the impedance wouldn't u have to increase the gains and would work the system more?

 

^^^ Gotta agree with nebster here, unless we rocketgyrl's post wrong, increasing resistance (impedance) would increase the amount of energy needed to produce sound. And more power = more heat in this case.