@mr-ed I looked at the manual for your MSI board. You have to make sure that Fast Boot is Off. I see that your setting for secure boot mode is set to Custom. That means that the keys can be loaded manually for secure boot instead of the standard setting which loads them from Bios. Secure boot has to be disabled which i think you said you have done but the keys have to be removed or unloaded as they call it.
So what i’m saying is:
Secure Boot Off
Fast Boot Off
Secure Keys Unloaded
Then you should not have any problem booting Antergos on usb. When you boot Antergos on usb you can try live usb and if that doesn’t work choose cd/dvd instead. It seems to work when live usb doesn’t. You may have other issues depending on what graphics adapter you have. But start from here and well see. You won’t have success booting if fast boot is not off and keys unloaded even if secure boot is off. All settings need to be this way.