The ZIP file format is also not the issue.
“Home → Games → /path/to/rom” easily opens the ZIP-file and displays the containing SFC-file. But when I try to open the SFC-file, I get the error I quoted.
I also tried unzipping the ZIP externally and putting the SFC-file directly into the folder. But opening that, again, gives the same error.
Thanks for the link to Retroplayer (Emulators list), but I cannot find the answer to my question there. How do I play the ROM with Snes9x?
Shouldn’t “Home → Games → Game add-ons” have content and browse through either Emulators, Contoles or Games? But it’s empty.