Nothing at the moment.
Have you used the 6U adapters personally? Are they any scratchier than stock when installed?
I did use them myself in a HHKB Professional 2 (non-S). Personally, even unlubed, they felt like stock and, once lubed, the feel increased a bit, but the thock was something else honestly (like Topre-thocky but turned up to 11). However, I assume that’s because of the brass plungers. If you were to use also “smoothest fine detail” plungers, I guess they would not feel that good however much lube you used.