You can control both car PC and car stereo with steering wheel controls using BSGc.
BSGc(Button Signal Generator CAN) is an external device connected through J2P BUS.

Even though the steering wheel control button is not CAN BUS, CPJexc can generate CAN signal to control the CAN BUS radio with BSGc.

CPJexc firmware newer than 160228 does not supports old BSGc.
New BSGc supports online firmware update.
This user guide is described based on new BSGc.
If you have old BSGc, contact www.exInterface.com to exchange it with a new one.