Luc, as others have indicated, simply looking at the volume control settings in different setups doesn't give an accurate picture of the actual volume that the listeners are experiencing in their different rooms. An SPL meter is very useful for this, and regardless of the volume settings used in a particular setup to reach it, an 80dB average listening level can be considered as being comfortably loud. Listening at a louder level than this on a prolonged basis isn't a good idea from the standpoint of hearing loss. Listening at an average of maybe 70dB is more advisable long-term and certainly isn't too low in level(the average level of conversation with someone nearby, for example, is about 60dB).
