In order to play the triton and the MPC so you are using the MPC as the sequencer and playing the TRITON keys, you need a DJ Mixer (or mixing board) and 2 MIDI cables. Take the outputs (RCA Wire) for both machines and plug them into your channels on the mixer or mixing board. Now take your MIDI cables and go from the MIDI IN on your MPC, to the MIDI OUT on the Triton. Take the second MIDI cable and go from the MIDI IN on the Triton to the MIDI OUT on the MPC.
It's basically OUT to IN, IN to OUT for each machine, but you NEED 2 cables, not just one. Now you can use the machines for what you were talking about. Everything will be heard through the mixer though, do not look at each machine or have headphones in one or the other because it wont work. Use the headphones and plug them into your mixing board or DJ mixer, I use a DJ mixer but a "MIXER" period will work.
Good luck and have fun!