It doesn't matter what the number is if the volume is good to you and distortion is within acceptable limits (e.g. you aren't clipping, etc.). It varies depending on all of your other stuff.. receiver, speakers, speaker/room setup, your listening point, your source itself (not just the hardware but the recording too), etc. It's not even possible to calibrate it except for a very specific set of criteria - the calibration would NOT hold for anything you watched or listened to. I mention this because every time I talk about how the volume control is relative - and it is - people come in with their favorite response, "Calibrate it!" Even if you calibrated it, if you just watch a different movie, or watch it from the couch instead of the chair, your calibration is no longer true and it becomes useless.
This applies to the speaker channel level adjustments also. They work the same way just that they are for individual channels and the number you set isn't shown on the front panel (but it will likely just change the maximum main volume such that the overall maximum gain is the same).
"Vintage" is good for wine, not for A/V equipment.