Do you have (a) another way of checking whether the outputs from the empeg are good, and/or (b) another line-level source to plug into that amp to see if it's the amp's fault?

(You need to narrow down the source of the problem via a process of elimination.)

Also, are the cables running to the amp damaged anywhere along their length (such as a sharp metal edge cutting them), or are they touching metal somewhere so that their shrouds are grounded to the chassis?

Also, have you checked to see if the wires have pulled out of the back of the sled? Some docking connectors had that problem.