Oh my god Guys... it seems like most of you dont have any idea about what the audio config is for...
Let me explain the correct and way better solution than adding another soundsource to your scene... and some other details...
After installing "Soundtrack by Twitch" there is an audio-source added to your OBS called "VOD AUDIO FOR SOUNDTRACK".
You just have to read, guys. This is the track transmitted as the VOD Audio.
Now when we take a look at the checkboxes, we will see that "Desktop Audio" is not checked. This is done by Soundtrack. Because it usually plays via "desktop audio" (what really sucks... to be honest). So when you're not using Voicemeeter, then you have got 2 Options: Get rid of Soundtrack or reinclude Desktop Audio by checking the box at track 6.
If you want all things to be like "without Soundtrack" you have to disable the VOD Track in the Options... Simply go to "Output" and uncheck "TWITCH-VOD-TRACK".
Et voila, the different VOD-Audio is gone. If you are using Voicemeeter i suggest you tell Soundtrack to send Audio to the "VB-Cable" or "Voicemeeter AUX Input". You can do this via Windows 10 Audio Settings... Rightclick Speaker in the "Systemtray" (thats the bottom right corner... in most cases...) and click on "open Sound-Settings" or whatever it says in english... then scroll down to advanced sound options and click it. Now you see this window (yeah i know... yours might be in a different language :P):
Here you can change the OUTPUT (its always the upper option) and the INPUT (lower option) for a specific program. MAYBE you have to enable Hardware encoding in "Soundtrack by Twitch" to make it appear in this menu.
Well that's all about this stuff. Hope this will help you to better understand what the settings are for and how to solve this issue with ST by Twitch.
EDIT: There was one thing i forgot to mention... i assume, that Soundtrack is NOT supposed to send its audio to desktop... i think in the beginning it was planned to add a virtual audio-device to the programm that's streaming the music right to the "VOD for Soundtrack by Twitch" Source... and the developers just lot it on the way to releasing it... :P So in short: i guess its a bug. No professional software engineer with streaming experience would EVER include include the music stream in the desktop audio and cut this whole sound out of the VOD... that's pretty BS... ^^
But MAYBE its working properly anywhere on a system in the open wilds of the internet... let me know if your Setup works different / without this "bug".