bflat
Headphoneus Supremus
Probably safe to assume it is the same as the IEMatch, but it would be good to have confirmation before I start soldering.
https://ifi-audio.com/portfolio-view/accessory-iematch/
Correct, that is the only pinout that allows both SE and Balanced to work from the same jack. The pinout between SE and Balanced are identical, except balanced splits the single GND collar to separate L- and R-. Also note, that AK 2.5mm TRRS is completely different pinout.