The outputs use standard TRS pinout (Tip = +, Ring = -, Sleeve = ground). According to the Head Amp manual the inputs are as follows:
Rear Balanced Inputs and Outputs: Tip = Pos (+), Ring = Neg (-), Sleeve = Ground
Rear Stereo Aux 1/4-inch Inputs: Tip = Left, Ring = Right, Sleeve = Ground
Front Direct 1/4-inch Input: Tip = Left, Ring = Right, Sleeve = Ground
If using the balanced inputs use a TRS cable (2 cables needed for stereo). If using the stereo inputs (unbalanced), you need a cable with 2 TS connectors and a TRS connector setup as follows:
TS Left Tip → TRS Tip
TS Left Sleeve → TRS Sleeve
TS Right Tip → TRS Ring
TS Right Sleeve → TRS Sleeve
A common TRS insert cable should work for this.