Setting Levels to 0.0 DB

Option click on the Channel strip fader will rest it to zero. Option click on the Pan control will reset it to center. You can move all the volume controls in unison by rubberbanding any number of channel strips but they will all move relative to one another so option clicking will not reset them all to zero unless they were all previously set to the exact same value. Pan reset is independent per channel strip regardless of what is selected. There may be a better answer to this but so far I haven't found a way to accomplish exactly what you're asking.

No can do!

HL

not one click, but two (at least for volume):

rubberband all channels
find the one with the highest value
drag it down to infinite
Option click

there might be a way for Pan too..

cheers
Martin