Do you have tweeters inside of your door mirrors? Just trying to ascertain whether you have the base stereo or hifi system. I suspect you have hifi as your car is MY2006.
The speakers/amp are certainly the weak link in the OEM systems. The OEM HU can be used to create amazing systems, and has been by many members.
I also looked at HU replacement but I went off it as i found out that I would've lost most of my idrive functions, and i dont think you can get software updates from BMW as well. Plus i like the OEM look.
2008 E92 335D SE - Ohlins
2010 E90 320D SE
1994 E36 318I SE
1996 E36 316I SE