Hi there i need a lil help picking an aftermarket Mp3 player for the A3.

At the moment i have the A3 concert system which consist of the SUb-woofer at the back boot as well as the Cd changer.

I would like to find a suitable Mp3 player which lets me keep the Cd changer as well as the Sub in the back but will also let me put an additional sub if needed?

Any advice ?

Many thanks