Out of curiosity, when you guys say your 64audio iems pairs up great with a particular source, what other source/s are you comparing it to? Would be good to know for a comparison reference.
Personally, I haven't find too many bad pair ups, unless if we are talking about non-LID ones like U18t/Fourte driven by original Hiby R6 with its 10 ohm output impedance where you need to use iEMatch. And also some portable sources will exhibit low level "waterfall" hissing with low impedance U18t/Fourte when you are idling or during quiet passages of the song. I mean, there will be some variations in pair up synergy, depending on sound sig and technical performance of the source, but either SPK, LPGT, WM1Z, DX220, Plenue L, N8/N6ii are all great.