Grant, from your latest description, power has nothing to do with the situation. If some source material happens to have a lower voltage output than others, obviously the volume control on the receiver has to be set higher(cutting off less of the incoming voltage)to get the same power output(not more)from the receiver. There's absolutely nothing wrong with turning the volume control up, that's the way it's designed to be used with lower output sources. You don't actually have a power output question.
Apparently your DG910 isn't aware that it's connected to speakers rated at 4ohms while it's only officially rated for 8ohms, so it's been doing a fine job.
