BMW X6 2009 Base audio upgrade

Hey Guys, first time poster here.

I just got myself a BMW x6 xDrive 35i 2009 with the DVD based nav iDrive system, and I find the Base audio really poor.

After reading up a bit on the subject I have the following shopping list prepared and I wonder if anyone can give me some feedback and/or help me out with some of the questions.

Hifi coding of my Base system
JBL-MS8 <- will I need a dedicated harness for this?
Jehenert flatline kit for front doors and underseat.
Sound deadening on doors.

Am I correct in thinking that the MS8 does not provide sufficent power? suitable small footprint amp suggestion?

Depending on how this turns out I might go for a Subwoofer in the trunk. Not sure here what to go for but the end result has to be stealthy and reversable. Any suggestions?

Finally, is there any point in moving the current speaker to the rear doors and/or shall I bother adding a center speaker to the dashboard?

Thanks for help

RobboD