I've heard very good things about Bavarian Soundwerks' upgrade kits.
http://www.bavariansoundwerks.com/
Although they don't yet have products for the F10, they are in the works and will definitely be coming at some point. To get an idea, you can look at the E60 speaker upgrade kit they offer as well as the amplifier upgrade. The speaker kits are drop-in upgrades and are very easy to install.