we're a cover rock/pop/alt band and have used the xovr mode successfully for smaller indoor shows when we have limited room, want to use one amp, don't want to bring our crossover and sub amp to save space and setup time.
the mode takes the signal from the board and sends lows to 1 and highs to 2. i believe the true application intended for the xti crossover mode is to have 2 xti amps in xovr mode - one driving each side for channel 1 and 2. with 2 amps you would have a a true stereo signal going to high/low left and high low right.
if you use one amp in xovr you won't get a stereo mix. when we have used the one amp solution we daisy chain the mains together off 2 and use one sub. in this setup you have a dual mono setup that is actually very clear because you flood the audience with two mono outputs out the mains. it's mono so panning and stereo effects don't work. i also found that the inputs are only taking one (channel 1) since it is intended for a single channel mono setup.
when you use band manager you can dial in the crossover point and might want to experiment. there are no rules with the crossover point. with 100 you do get a good starting point. we actually set it a bit higher (200) because we run 2 synths and bass through the board and find that we clean up our mix by getting the lows out of the mains.