Hey,
What you are doing is known as 'daisy chaining'.
This can be complicated...you are basically starting the chain at the MPC and thru'ing all the way to the XV5050, where it gets sent back to the MPC. Look at the top diagram to imagine it.
My understanding is that Thru ports DO NOT send information that is sent to the Out port, they only mirror what is sent into the In port.
This would mean that you'll have to find another solution. How about connecting the Triton's out to the MPC's in? That way, when you play the Triton, the notes get sent out its Out port and into the MPC's In port where they can be recorded (make sure to have the local turned off on the Triton). Look at the bottom diagram to imagine it.
Take care,
Nick
PS: This is exactly what Bigdmakintrax said, I misread what he had written.