Ah! Okay. And I got the videos now. You didn't add Voicemeeter just because of that, did you? Gain structure is about managing what you already have, not adding more.
Looking at the videos, I see that you're using a Noise Suppressor.
- Are you asking why the music still gets through it? Noise suppressors aren't perfect, especially when what they're trying to remove keeps changing, like music does.
- Or are you asking why the music sounds bad through it? Noise suppressors are usually designed for voice, including this one, and so they often treat music as noise to be removed.
Or are you asking why the music is in the mic input at all? You say you're using headphones, but like I said at first, are you sure the 'phones aren't bleeding acoustically into the mic?
Also, what are the settings for those audio sources in OBS? I *assume* that you've connected them correctly, but it doesn't hurt to make sure. I don't see a way for the settings that you show in Voicemeeter to bleed like that.