I think the 75 db might be the standard to allow for headroom of various speaker sensitivities in a system and still achieve the 85db movie standard.

I guess you could clibrate to 70 while using the disc and then to 75 when using the pink noise from the receiver, as the receivers output is set at 75db. The biggest thing is maintain the same speaker levels all around.

Jason
M80 v2
VP160 v3
QS8 v2
PB13 Ultra
Denon 3808
Samsung 85" Q70