Want to upgrade audio in my new 07 S80
 

I am the new owner of a very nice and well kept 2007 S80 3.2 with the Dynaudio system. In most respects I am very happy with the car. The Dynaudio system has a great sound when playing music with very little bass. I can hear dynamics and sounds that I didn't even register in my old car. However even turned up all the way it isn't very loud, and any song with even a decent amount of bass starts distorting the speakers badly.

I want to upgrade but I do not want to change out the factory headunit. Don't want to mess up the nice clean look and of course the steering wheel controls, climate controls, Sirius, etc., are all built into the factory head.

Did a little research and it seems like I will need one of these digital signal processors in order to hook up amps to the head unit. How would that work? Would I no longer use the amp under the driver seat? Would I need to change out the speakers and amp them separately? I assume I would at least need an amp and a separate sub. Do any companies make subs that fit into the trunk that would maintain a factory look?

I guess I just need someone to guide me through the process. I guess my main goal is to get the bass out of the speakers, and add a sub to support the bass. Don't know if I need to replace the speakers and power all of them with an amp as well. Also interested in adding a source to attach a flash drive. Thanks in advance for any advice.

Oh and another question--do any of you get this humming noise any time you even select "Aux" as an option? I don't even have to have anything plugged in for this to happen. When I start playing a song through my phone for instance, the noise disappears, but reappears when the song stops.