I just ran the same sets of experiments with my DVD player hooked up to optical1, input mode set to stereo, and CD as source. Sure enough, I could hear the hiss when the CD was paused, and I could hear the hiss on the switch from -80dB to -79dB as well.

The hiss was faint and I don't think I could hear it from more than a few feet away, but it's definitely there. (Prior to upping the volume from -80 to -79, I couldn't hear any background noise, which is usual for my system, so the hiss is obvious, especially when the CD is paused, or skipping between tracks, etc.)

I didn't try any of the other experiments but I have little doubt the results would be the same.