I would agree that it’s definitely not a food reference. I have heard a lot of different speakers and these are The only ones I have heard do this.
Just like you described it. There is a quietness or darkness around each instrument that makes it stand out.
I don’t think it’s in the treble at all because it’s in the whole range of the speaker.
It sounds like you won't be happy with anything else except for the 804D.
Just add some great subwoofers, set the speakers to small, XO to 80Hz-120Hz (since you don't want to abuse your Diamond speakers too much), never go crazy on volume (again, you don't want to abuse your Diamonds) and you are set.
Back when I had the 802D2, I also set the speakers to Small, XO to 120Hz, and let my dual Subs do all the heavy bass abuse. No way I was taking any risks with my Diamonds.