Sound system upgrade for cls 55 amg

[Peanut Budda]

I have been eyeing these up on eBay for a while and my main worry in retaining the menu options and steering wheel controls.

They seem a bit to good to be true given what is packed into them so i'm quite interested if any one has fitted one.

I have looked at command online but they are too expensive for me to upgrade to COMAND NTG2.5.

Whilst I know you can do both which should you do if only doing one?
The panel that the actual speaker sits on or the panel that is actually the outside skin of the car?