When trying to use it, however, I get an error that suggests that the app needs all input devices exclusively, and that I need to run it without e.g. LXDE.
X is still running. Please shut down X in order to mitigate problems with losing keyboard input. For example, log out of LXDE
So, I try logging out and get to a login screen. One of them is 'default xSession', which sounds like what I want, but when I log on to that I get bumped back to LXDE.
tl;dr - how do I boot to command line? Or, am I way off in my solution to this problem?