Disregard my previous post about the PAC Audio products. They seem to complicated and I'm unsure if it will retain RAP and interface with the Class 2 Data Bus.
These are the products we use at my shop, without any problems.
Use this instead:
Also this is a quote from the Application guide:
"These vehicles have a "Premium Bose®" amp that only accepts 2 channel audio inputs. OnStar® volume can be controlled via the steering wheel audio controls. The GMAHCM chime module is not required when using the BOSE® amplifier.
If you are not using the BOSE® amplifier, then the GMAH24 and GMAHCM interfaces are required. The aftermarket radio will not fade, however it will still continue to balance."