you can only do each trial once and each one gives you a single orb... there are two machines that take orbs, one is a lift device going down to lower levels and the other opens a door

killing guards in the tower depends on what choice you make after opening/ entering that second door area... its a point of not return and you MAKE YOUR CHOICE once inside


Luke Skywalker: I don't, I don't believe it.
Yoda: That is why you failed.