Was I wrong in thinking the MPC had a phono amp also?
I don't mean to discourage the purchase of a mixer. With a setup that is likely to expand, mixers are always great to have. I always encourage the purchase of a mixer for routing, monitoring, and recording where applicable.
You always want to keep the signal chain short but it shouldn't hurt much to have the mixer there though. The reason why I recommended going straight from one thing to another is because if that's the only reason is was going to be used for, then a mixer was unnecesary. If you have multiple devices that you might record into the MPC, then a mixer is good to have though.