I realized there is a more serious problem here - there doesn't seem to be a way to get the guitar input to the DAW without also playing it though the speaker. Turning the mix volume down on the Amplifi turns down the guitar signal going into the USB as well as the playback through the speaker (so if you turn it all the way down, there is no guitar input.)
It seems it would be more useful if the guitar volume into the DAW was fixed independently of that setting. (I suppose if there was a dry input it could have that property.)
As things stand I don't think I can use the Amplify as DAW interface. (I would be interested if anybody else figured out how to make this work.) Too bad, as it seems like having a laptop, a guitar, and an Amplifi would have been a pretty versatile portable combination.