I do not know what custom stands from Star Sound would cost or look like, but I feel it would be worth exploring.
It looks like you own or have owned Star Sound products. If you like the Star Sound products that you have tried, and if you like the sonic attributes of the Grand Prix stands (which I imagine you do since you own them), you might also like something from Star Sound for your speakers.
I owned at the same time the Star Sound Apprentice stands and the Grand Prix Monaco amp stands (Apex footers, silicon nitrate balls, and the thicker acrylic shelves). I tried both under my floorstanding speakers and they are similar in the way they enhance detail retrieval. Both products are very good.
One thing in my system that my Star Sound platforms do that the Grand Prix stands did not do, and which I cannot really explain, is that the Star Sound platforms really help in creating the illusion of my speakers completely disappearing. With the Apprentice stands, I cannot tell that sound is coming from my speakers; instead I am hearing a more seamless, wide and deep soundstage. Your monitor speakers might already do that, so maybe Star Sound stands would not help in that respect, but for my floorstanders, the Apprentice stands were a revelation.
Tom