dj750 cue / djm2000 cue

I went to a friends the other day and he has a djm 750 but i could not seem to get the headphone cue working,

can someone explain the difference between the cue on my djm2000 and his djm750

with my djm2k i press the master cue and then select the channel i need to cue on my headphones and the headphone mixing cue to prepare my next track,

for the life of me i could not do this with his 750?

what am i missing?