How do I turn off the amp sims in Garage Band?

I am trying to record simple guitar and drum tracks using a Steinberg UR22 MkII. I'm taking a line out from my amp, going in to the UR22, then into the Mac using USB.

I want to record tracks using only the signal from my amp but don't seem to be able to turn off the amp sims, so I am having to use either the vocal mic settings, or a clean amp sim. Both colour the sound somewhat, which is definitely not what I want.

I also want to record drums from an electronic drum kit using the same method, and similarly I want the native drum sound to not be coloured by sims and effects.