@Mike-B - the top two shelves are bamboo on bronze spike upgrades, which I’m told give the benefit that the QPlus Ref feet otherwise would. I heard this for myself in an A/B comparison of the 552 head unit on the top of brain rack, then again with the head unit on the next shelf down but with the QPlus in place when my dealer and I could hear no performance difference. This experience was consistent with the advice that my dealer gained from his contact with the design guy at Quadraspire.
The reason for trying these things in the first place was I wanted to demo a CD555, which had to be on the top shelf where my 552 previously sat, and my dealer and I didn’t want the performance of the 552 to be compromised by moving it down the rack onto an ‘inferior’ shelf. The QPlus solved that. The next set of experiments took place over a couple of weeks on each of the 300 head unit, its PSU and finally the 555PSDR ie each black box on the normal SVT shelf and then with the QPlus in place.