Gain Setting impact on AV processor DSP Quality?

I have a nad AV processor and recently began using the DSP and the results were quite remarkable.  After what appeared to be very minor changes to the overall curve, ie smoothing it out and getting rid of some jagged activity, the tonality and vibrance improved substantially.

I'm trying to understand what caused all this to happen. I know there's gain settings within the DSP which I really didn't fool with, I only changed the level adjustments for each of the speaker channels.  Possibly could gain adjustments within whatever happens inside the DSP have impacted the overall quality of what I'm listening to?

I don't have any way to adjust DSP on my pre-amplifier which is used for two channel listening and that sounds pretty good without DSP. Maybe DSP would impact my two channel listening.

But for now I'm just wondering why the Quality improved so much and whether the gain setting had anything to do with it. And how would adjustments occur within the DSP capability of the AV processor? The AV processor doesn't have separate gain Controls.