Examples and suggestions for after-market sound systems

[dogdrool]

Has anybody out there improved the stock (or "premium") sound systems in their X5? If so, can you share your setup and experience? I want to upgrade the sound system, but I want it to appear stock. For example, I don't want to put a giant sub-woofer box in the back or something crazy like that.

Also, I live in Colorado. Any suggestions on a great shop to get the work done?

Thanks.