Yes, thanks, thought there was a model of avr beyond the HTIB model designation, that's how Onkyo usually does it. It doesn't appear you have a choice of volume scale from perusing the manual and at a guess it pegs reference level somewhere around a volume reading of 82-85, altho the manual doesn't specify (and this would be relevant for movies, not music so much).
The specs you posted for the speakers don't indicate a sensitivity rating for the stock speakers, and a fairly low sensitivity (of 86 dB) for the Onkyo 4800s. To get the most out of the amp, i.e. louder levels with your speakers, you'd need more sensitive speakers (which is the spec that somewhat indicates how loud your speakers can get with a given amount of power).
Before changing speakers, is it possible to return the whole HTIB set and buy separate components?