I have '01 X5 3.0i with sport package and self-leveling rear air suspension. I need to replace all four shocks. After looking around for a while, I think only ACS Sport Suspension is the only aftermarket shock that works with rear air suspension; however, the kit is expensive. I have several questions that need your opinion:

1. If I change all four shocks with OEM shocks, is it a good idea to lower the X5 with HR spring or Eibach spring?

2. Is it a good idea to mix/match shock, for example replacing front shocks with Bilstein HD shocks and replacing rear shocks with new OEM shocks, then lower the X5 with either HR spring or Eibach spring?

Thank you very much for your help.

Justin.