2009 C70 how to add Amp to non-Dyno setup
 

Situation is I have a non-Dyno stereo setup and I want more volume, the stock 160Watt x 4 channel amp is not cutting it..local audio shop says only way is to use a line level converter and install an amp in line after the stock AMP..any suggestions on this setup..honestly volume is fine with top up but as soon as top is down to weak for my liking.

Someone suggested trying to find the Dyno amp and switch amps..any thoughts on this..will it work?

Thanks in advance for your help