@carrion Yes it does use the default config if you have one. I'm thinking probably it shouldn't. However you should still be able to override options with emuargs as this takes priority.
You say you can't pass any arguments. Can you share your launch config? This should contain an array of string arguments, the same as if you were starting fs-uae from the command line. e.g.
Code:
"emuargs": ["--floppy_drive_0_sounds=off", "--fast_memory=16384"]
If you're already setting the 'fastmem' option this might conflict, so remove that if you want to set it via 'emuargs'.