i use both alot, mpc/master -fantom/slave = making beats on mpc and playing keys on Fantom; Then Fantom/Master -MPC/Slave = Using the Fantom to make beats and play parts on the Mpc Or Use the Phantom To track out my Mpc Tracks to The Audio Track Expansion applying effects and mastering then layering more parts from the Fantom, either way is ok, yes you will be able to hear both units once you get the mixer and the way i told you to set it up, over here im having fun with this setup and once you get it you be okay, my best advice is to read-read-read, the sequencer on both are great to me, since i been rocking the mpc for few im comfortable using it and applying the same experience to the Fantom X which i only had for 2 weeks, pretty much there are the same to me, both has its limits, im not no debate dude, so i run with what i buy and learn it and dont complain. I hope this Helps You to a great deal and others, this is how im getting down for 06 with this setup, it seems to work for what i do.
Peace Synagodz