The speaker channel levels may also be set below 0.0dB, which was the case with DenPureSound when he complained to me that his amp was "underpowered". When I told him to increase the channel levels to 0.0, everything seemed peachy.
For some sources, like my weird Apple TV, I have to also increase the Denon Source Level by +6.0 in order to match the other source levels. Otherwise, it would be 6dB less than everything else. It's probably not the case w/ the OP, but just giving an example of the 2 areas where the levels may need to be adjusted:
1) Speaker Channel Level
2) Source Level