I am getting my 323i sport/nav in 9 days. I plan to install the cd changer in the trunk myself (thanks to those who posted such good install pics). I see that the standard sound system amp is right below the nav unit in the trunk. It would be easy to replace the amp at the same time if a different amp 1.Installed with no hassle. and 2.Made a significant difference in the sound quality.(I listen to classical mostly). Anyone have any advice for me?