I know Miki is a proponent of never mixing oils, and I’d agree that it’s the safe answer. With that said, I’ve mixed oil several times in my personal skis after testing the oils fairly extensively. I’ve never used the Amsoil, so I can’t speak to whether those particular ones cause gelling or not though, and the testing process is not quick enough to be worthwhile unless you are planning on switching permanently... Going back and forth is never a good idea, so you need to decide whether you’re going to order XPS in the future, or start using the Amsoil exclusively...