The last two are only for reverb. (Why in the sweet name of sanity was that choice made??)
This just isn’t true…you are stating something as fact presumably based either on your own inability to operate this thing or on a faulty unit…the guy posting about logic has done exactly what you claimed before is not possible.
EDIT: Sorry to be clear…what he has done is route to another out (as you originally wanted to do). He may not have used what you refer to as “the last two” but only you can know that…and regardless, none of the outs are only for reverb…the main outs and outs 1, 2 are a clone of each other and the others are configurable as a separate pair or mono outs.
The unit is called UR44 pretty obviously because it is a 4 channel i/o interface…the extra 2 are admittedly adding more confusion than usefulness but you can still achieve what you were originally trying to do with the 3rd or 4th output and inputs.