Quote:

All of the speaker(s) volumes, except the sub, are controlled by the amount of watts they get from turning the volume knob on the receiver up or down.



No. When you change the main volume, the sub's volume should change too. The main volume acts universally across all channels including the sub.

Quote:

The line level from the receiver to the sub remains at 10 and it does not change no matter what the volume on the receiver is set at.



No. See my previous comment.

Quote:

Also, the volume knob on the sub itself remains static at 7 no matter what the receiver's volume is set at.



Agreed.