Are you sure that's the core that works?
https://photos.app.goo.gl/hbyXfgMiU166a6E82
EDIT: Still haven't manage to get the lynx core working but, to anyone interested in this, I got the core to save as a DIFFERENT core.
I'll try to explain what I did. It's pretty simple but somewhat cumbersome.
First, I created the number of copies I needed of the core, changed their names accordingly, created their corresponding .info files. Simple stuff. Then, I went and hex edited the internal name of the core (any hex editor will do) to the name I've given to the core. (IN my case, I did a search for "Genesis Plus GX" and swapped it for whatever I was trying to emulate with it)
Presto! just like that it creates its own config folder with the name I gave it.. I hope I haven't mess up anything by doing so :S But it seems to work so far... If anyone else tries it let me know if it works or not.
If it does maybe OP should consider it adding to the OP?
Thanks
UPDATE: No, don't do it. It works on the PC cores but not on the Wii U. It breaks the core (memory error from Wii U)
Back to square one...