Yes, like the rest of the speakers, the sub should be set to 75 dB...................................at first. Once you've got all the speakers (sub included) matched at 75 dB, adjust to your personal taste. I run my sub hotter, and my center a couple of dB hotter.
Regarding where to set the receiver's volume knob when calibrating: There should be some indication of your receiver's reference point. My Onkyo allows me to select one of two scales for my volume readout. One scale ranges from 0 (no volume) to 100. As I go up the scale it reads 80, 81, REF, 83 84, etc. So, obviously 82 is the reference point, and where I set my receiver when I calibrate to 75.
The other scale runs from -82dB to +18dB, 0 being the reference point. While it is not necessary to set your receiver at it's reference point when calibrating, I think it's a good idea.
