Correct coil springs combined with matching struts and shocks are superior to air ride, not to mention way less problematic IMO.
Anytime you use lowering springs of course the ride will be on a harsh side.
People complain about Bilstein HD but after matching them with stock coil springs, the ride is absolutely awesome.
$30 will take care of that warning light.
http://www.xoutpost.com/bmw-sav-foru...gs-delete.html