I'd use only the alpha from the metal image texture and set the metal color in the Metal shader directly.

Thanks for the tip! I tried it, but it just made it all one colour or all overexposed. I also tried an add shader, which seemed to work at first, but I couldn't see any actual metal shader. Here's my current setup:

The image texture on the bottom right is the metalness map by the way.

No need to answer this problem currently, I just bought the Advanced Template. 😋