That looks really sharp, and I'm assuming that the sound is leaving you grinning uncontrollably!
Louis did nice work matching the veneer from the mains down to the subs. Great detail!
Regardless of one's speakers, more subs helps mitigate room modes. If I've learned one thing in audio, it's that the more I address the room, the better my speakers sound - regardless of model! If you have the flexibility, you may want to consider whether moving the F12s around the room a bit can even out your bass even more. After you just enjoy your system for a while, of course!
(I have a similar 'stack' approach with my mains sitting on top of subs utilizing opposed 8" Rythmik drivers. In my case, Robert Herbelin recommended five Big Fat Dots to separate them, though I admit that I'd prefer the look of a smaller reveal as enabled by thinner Dots than my 1/4" Fat Dots. I replaced my Herbie's sliders with another product, but like you, I was amazed at the difference obtained by isolating the stack from my suspended wood floor.)
By "Furutech disconnects", are you referring to the FT-210 tab style disconnects? I've looked those up online several times but never quite pulled the trigger. (My drivers are well suited for their application, but the spring clips they use are not exactly the best mechanical connection ever invented.)
Where in the world did you source pieces of petrified wood that large?
Again, nice job!