First, the speaker load has everything to do with overheating the amplifier.
You are probably overloading it.
Second, It's LOUD TECHNOLOGY that markets these things, and they don't support them too much. You won't find a module for sale by itself. They will sometimes provide schematics.
However, might be repairable, post this question in:http://music-electronics-forum.com/
to find a mackie tech...this MEF has a lot of techs that can help you.http://music-electronics-forum.com/f22/