I highly recommend Reid Vann
on Manchester/McKnight. I'm sure they would offer lower install prices if you have BMW CCA membership. But you'd have to call to confirm. I've had work done on a VW after a horrible suspension attempt and the owner was willing to show me what I did wrong prior to fixing it for me and explained all my suspension settings.
I find it rare to have this level of customer service, and to not be talked down upon how some shops do.