I would also add, set yourself an upper limit on the volume knob and NEVER go past it. You mention the scale goes from 0-30. I would select say 25 and never push the volume past that point.
As you push a receiver/amp near that 90% and beyond mark, you are approaching its near max capability. Do not risk distortion due to the limits of the amp.
The volume it plays at 25 on your receiver is irrelevant. If you want more volume, get a more powerful amp/receiver. Even then, if the amp will outpower the speaker, you will get some maximum excursion noises instead if you crank up the volume too far (e.g. the speaker driver hitting the point at which it physically travels no further).
Again, this point would be damaging as well, but more physically as opposed to electrically.
If after all that you still want more volume, break out the piggy bank and buy a bigger set of speakers (or add more to the system).
