Bruno, I am not quite sure which way Audyssey does it, but I believe most calibration routines will set one of the front speakers at a 0dB gain on the receiver. Then every other speaker is gained up or down relative to the 0dB speaker to make them all the same output with the same test tone.
So to answer your question I would 1)find the 0dB speaker, 2)play a test tone and adjust receiver volume with that speaker so it reads 75dB or 80 dB (you pick, whatever is easy to read on your meter) then 3)cycle through the speakers and see that each records the same dB output.
Now a little trick I use you might find useful - I set the 0dB speaker to be the center channel and then set all other speakers relative to that. That makes it easy for me to see if I have the center channel bumped up a few dB for movies or not. For multichannel music listening I like the whole system flat, but for movies I sometimes up the center as many others do for dialogue. Hope that helps.
