The correct way to do a calibration is to have a reference speaker. In this example lets say the left main is the reference speaker, this speaker should be at 0db trim, but should be at 75db on the SPL meter. To do this, you need to use the main volume to get your left speaker to 75db.
Once your reference speaker is done, proceed to do the other speakers, matching your reference speaker using the trims for each speaker (not the master volume like you did with the reference speaker).
Does this make sense?
