Yamaha htr-5550 Main speaker output level?

Looking for some help on this....I'm looking thru the manual and it has a section on speaker output levels, and it has you go to the test tone button and as it goes from speaker to speaker in the test tone mode, it tells you you can adjust their output, when it goes to the Right Main and Left Main, the book tells me to adjust with the volume level, but it doesn't seem like it does anything, it raises the volume of the test tone for all the speakers, whereas when you get to center and l, and R surrounds, it has you use one of the arrows and you can change the db's..

Also what DB should the subwoofer be set at, it has a -20 to 0 range..

THanks for any help, I'm just playing around and trying to get the most I can out of my system...

THanks,

Rick