I'm not sure how the 950 calibrates. With the 1050 I start with the front left main, set the master volume until my SPL meter reads 75db, and use the level trim (+/-db) for the center, surround and LFE channels. If the front left/right levels are not matched, I have to use the balance control to even those out. The sub is tricky, and usually calibrated to what sounds "right" to me. Reference level, I think, is the volume setting used to achieve the 75db calibration. So, if you set the volume to zero when calibrating, then zero would be reference level. Anyone have a better explanation please chime in(Gonk!).