Read the fitting guide!

The small black box (labelled 3 amp, actually) is the choke, which needs to be fitted in the empeg's red power line - it supresses ignition noise.

The other wires need to be put *at the amp end*, between the wires from the head unit and the amp line-in plugs, with the "small metal circle" (the ground tag) being connected to the amp's ground input. Do this for all 4 audio lines - there are two left/right pairs of cables.

Hugo