'04 X3 Radio problems (non NAV)

[04X34TRACY]

Hello,

We just recently purchased a 2004 X3 3.0i and we love it. The only problem is the buttons on the BMW Business CD radio unit are not working, except the volume knob and the CD eject button. We didn't notice this problem until after we bought the car. The only way we can change radio stations/change songs on a cd are by using the steering wheel buttons. Has anyone had this problem? Or has anyone installed an aftermarket stereo in their X3? The cost to replace the stock unit is about $750, so hoping to find a cheaper alternative...

Thanks!