Specially for people coming from other DAWs setting up a midi track and an instrument track in MOTU Digital Performer can seem somewhat confusing. Personally I like the way Digital Performer handles things. It work kinda like the way I am used to from big consoles. And in the case to mdi and virtual instruments I believe it is just way more flexible the Digital Performer is set up, as it is easy to route multiple midi channels to one instrument, and still maintain a logic structure of your project.
I made a short video on this topic - watch is on YouTube here: Midi routing to Virtual Instrument in MOTU Digital Performer