Cruncher, as casey pointed out, if you use a mode such as DPLIIx, it extracts ambience from the front channels which originally came from directions other than the front and sends it to the side and back surrounds. So yes, in a mode like that the surrounds work all the time.
As to sound level, very few would listen at "reference" as a standard procedure. For listening at home it's simply too loud, and a setting 10dB or so lower is commonly used. Whatever the level of the mains, the level in the surrounds when using an ambience extraction mode such as DPLIIx is somewhat lower, since the greater distance and reflections involved in that sound lowers its level.
