Grant, your comparison with the 80 watt Marantz receiver gives additional confirmation(and would have been helpful if mentioned earlier)to the point already established: that you already have ample power since some sources play at an adequately loud level. The similarly-powered Marantz played "much louder" with your low level sources because it applied a higher gain(most likely at the pre-amplifier stage)so that its full capacity could be brought into play.
Your DG910 might have an unusually low gain pre-amplification section, either by design or possibly because of a defect in your particular unit. If the latter, of course repair should be considered as a warranty matter. If the problem is inherent in the design you should consider a unit with similar maximum power capability but with higher gain for low-level source material. You know at least one that fits that description!
