Thanks for your reply!
Loading cassettes (.wav only) in MAME is working fine when typing the LOAD"1" command manually and the Return and ESC.
I own the real thing, so I know how it works and that's why I love to add it in LaunchBox.
I just thought to give this a chance in LaunchBox as it's very handy just putting auto-command lines.
I know that I've put "-cart" twice so that I can also run cart-only software directy, so it's not the problem here.
The issue here is that somehow it's stucking after the first letter "L" and then it skips to the return (\n) command, instead of typing LOAD"1". Maybe it needs some slowing down thingy, that it will type correctly?