I have found that with my Onkyo receiver, my SPL meter reads differently when I play back tones from a calibration DVD vs. the built-in tones -- and that's without adjusting the master volume. In other words, the levels do not match up when I measure the SPL of a DVD test tone against the level of the built-in test tone.

I'd rather calibrate from the source, since it's the DVD player is what's going to be playing all my movies.