.78 2 pin UTWS5. The fit is almost ideal. Was initially going to use a set of Moondrop Blessing 2, but the small divot made the connection weak. Same with the Truthear Zero. I narrowed my choices down to the Dioko or the S12, and the Dioko was a better fit all around. The Dioko's are also able to completely fit in the case without issues. It is almost like it was meant to be

Was looking for a way to reintegrate my Dioko's into my daily use and this Fiio wireless was ideal to put them back to work. So far,I am very happy with the volume levels and sound quality. Bonus: the nozzle lines up perfectly for my ears. A step in the right direction; although the case size is a deterrent. Glad I was able to find a use for these so that they don't get neglected.