[glaufman]

OK, that kinda makes sense, except, (and pardon me because I havne't fully thought this through...)

If the goal is to see room acoustics, then feeding the spdif into the avr, and feeding back the preamp out to the sc as a cal loop takes part of the AVr out of the equation... basically it takes the errors in the AVRs DAC out of the equation, so after cal adjustment, the measurements you see are TRUER representations of the ACOUSTIC response of the room, no?