Green LED indicates that what xDSD is getting from your MacBook isn't MQA. Quite possibly it's due to how your Tidal is set up, or what your Mac really sends out.
MQA by design has to go in its native form from an app to xDSD to engage magenta LED. Any data manipulation along the road, i.e. upsampling, filters etc. prevent this from happening. Magenta LED in your car shows that everything's in order there.
Also, please see here:
Your Denon used as an analog amp in your case has nothing to do with green LED on xDSD. As long as this amp makes sound on your speakers, you're good.
Pre out on your Denon allows you to use this amp's volume control for i.e. a separate power amp, so not useful considering what you want to do