If you have multiple MIDI OUTS on your computer: you run another midi cable from another MIDI OUT on your computer to the Triton's midi in
If you only have 1 MIDI OUT on your computer: it's been a while since I've done this, but I think you would plug a MIDI cable from the MPC's MIDI OUT to the TRITON's MIDI IN ... Then tell the MPC to send out MIDI CLOCK as well.. Where I show "SYNC IN" you also set SYNC OUT and you set that to 1 or 2 depending where you plugged the Triton. That SHOULD work... You press play on the computer > MPC syncs and starts > MPC tells the Triton to sync and start > Triton syncs and starts