I too find the Natural mode louder. But then the AM/FM selection is very loud. I have to turn the volume down to about 20 +/- for average listening. In the DD reference listening I have the volume turned to about 55. For DTS for the equivalent volume about 50. Ah such is life!
I once read on the forum something to the effect that "instead of enjoying the sound, the audiophile is constantly critquing the technical attributes of the sound....". Enjoy the music!!! Forget About It! What kind of cables do you use? What are your room acoustics? Are your speakers timbre matched? Where do you have your sub? Where is that darned sweet spot (G-Spot?)?