Well... let's say WAGNUS. should have an "unusually" close relationship to FitEar, just like that special chemistry between Yamamoto Sound Craft and Audio Technica. I guess that Suyama-san only allowed WAGNUS. to be their "exclusive partner" when it comes to making FitEar IEM/CIEM cables with their official pin connectors.
Kume-san posted a picture of his own pair of FitEar CIEM before and I also mentioned that here
He also placed his FitEar gears right next to PAD-SO (and some prototypes?) as shown in this picture
Bialbero Epsilon S should have impedance mismatch with those super-sensitive models from FitEar so that's pretty natural for him and Sugar Spector working on something together in order to take care of that. He seemed to be fan of Triad Audio before Bialbero PROTO1 was born.