Mad Scientist Audio's Graphene Contact Enhancer
Audiolab CDT6000 and Tweak Audio EVS 1200 power amp. Beast of an amp based on dual mono IcePower AS1 1200 modules and lots of tweaks. He made less than 20. What a bargain @ $2700.
Audio Alchemy DDP-1 + PS 5. Dac/Pre + outboard PS. I bought the DDP-1 used sans PS 5, and searched for 5 month for the power supply to no avail. Finally I contacted the manufacturer who had one left. The improvement was/is well worth the $600 he charged me
All 3 pieces have anchored a lot of ancillary improvements for 3+ years. The AA comes up occasionally make sure it comes with the PS