Thank you for getting back to me.
I found the issue:
I somehow managed to overlook the passage in the steam unity integration documentation, where it says that after applying steam geometry you have to do: Steam → Export Active Scene…
I did that and now it works =)
Exporting the Active Scene then automatically creates a new Gameobject named Steam Audio Static Mesh. Just mentioning this for the beginners, like me.
Thanks again, I was sure I would switch to DearVR. Now I am unsure again.
Issue is solved <3