this is what i have in my slk230 with bose amp and aftermarket becker 7990 head unit ... not sure whether your amp needs high voltage balanced inputs, but this will boost your line voltage to a maximum of 9v RMS, dial in the voltage to match your amplifier requirements; output can be set to balanced or unbalanced, my slk230 factory amp wants balanced (standard RCA is unbalanced)

http://www.audiocontrol.com/t34/6349...l-Control.html