Its all in the first post. Only difference is your rears may not be the quietest, which only means you'll have to turn down other gains.
Basically set the gains to the correct position (at 2v or use a DMM), then turn down the "louder" gains to match your quietest ones. Remember when you play pink noise to level match use a volume of -25db or lower.
After everything is matched, my advice would be find the MS-8 volume where the SPL is 55db (using the same method as above). Then use that as the calibration volume. If that doesnt sound right work down to 50db.
2008 E92 335D SE - Ohlins
2010 E90 320D SE
1994 E36 318I SE
1996 E36 316I SE