To quote "Setting a receiver's volume to the reference level is not the mystical task it often appears to be; in fact, a receiver's reference level is whatever your theater needs it to be."
In other words, whatever setting on your volume knob that gives you 75dB would be your reference level setting. A number of modern receivers have auto set-up routines and digital volume level readouts, and they will set themselves so that a reading of "0dB" is the reference level (75dB). On those receivers, any reading of less than 0dB (such as "-20dB") is quieter than that reference, and any reading higher than 0dB is louder. Older receivers, or any one with numbers printed around the volume knob, certainly may not have an output of 75dB when the volume reads 0dB (and a lot of receivers use other numbering schemes that don't include a "dB" marker). The actual output level depends on more than just the receiver - your speakers and your room are two major factors.
Anyway, don't worry about putting your receivers volume knob at some level and then trying to get 75dB. Get 75dB, and then you know what setting on the volume knob gives you that.