I'm surmising here, so don't jump all over me if I'm wrong, but I think you are being misled.
This article discusses why any DSP on DSD is pretty much a no go.
How do you know the DSD signal isn't being converted to PCM internally? Your player can put out DSD over HDMI, check. Your AVR can receive DSD it over HDMI, check. Your AVR can decode DSD over HDM, check. And in each case there is likely some indicator on the equipment that says what is being input and output. But once you engage DSP, things change, even if the equipment indicators don't
Why would Onkyo have a method for doing DSP on native DSD when no other manufactured does? And if they did have such a method, why wouldn't they be shouting about it as a selling point? I'll bet your owners manual never even mentions it one way or another except to say that the AVR will acccept DSD over HDMI.