Unfortunately, sound problems depending on operating systems cannot be debugged or fixed by addons.
This addon usually works on Linux, I checked it just recently on Mint 20.

It might be a problem caused by one or more of these points:
- OS/Driver Setttings
- Game Settings
- Playing on wrong sound interface/device (which might be not present), it might differ from the main interface sometimes (game bug)
- Settings of this Addon
- Bug in the game (Please seek game-dev support)
- Bug in BASS (sound library used by the game to stream sounds)
- Bug/Regression in OS/Driver (it happens in Linux-OSes sometimes after updates)

It seems to be a Game Problem because now i can hear ingame Sound only from Monitor Speakers but 3D Radio sound is comming from my headset

Yeah, it is a known but supposedly fixed bug in the game. Make sure your game is up to date. Sometimes the game used to mix up sound interfaces/devices, especially on hot plugin during the game's runtime. The devs fixed it a while ago, at least for Windows. Actually there are atleast two sound engines active: The Source Engine one and the BASS library. Source's sound engine does things quite fine. BASS however does not handle devices that well, because it is not that well integrated yet. This addon uses functions provided by the BASS library integration.

There is nothing I can do about. Please report the problem it to the G-Mod devs:
https://github.com/Facepunch/garrysmod-issues/

Mind their reporting rules, though.

Closed as resolved