EW play is multi-timbral like HALion so one MIDI channel equates to one track in Cubase (midi track). I believe that Cubase Artists allows for 32 VST instrument slots so you can run several tracks out of one Play VST instrument slot.
Example, I use MOR2 and The Dark Side Play libraries for drums, I'll have 2 MOR2 instances running 10 midi tracks in Cubase. Each having its own thing (channels 1-2 bass drum, 3-4, snare, etc...). Same channel numbers but coming from two different Play instances into two different MIDI tracks. I'll throw another Play VST into the project using 3 or 4 more tracks for FX from The Dark Side.
So there is around 14 tracks with but only using up 3 of the 32 VSTi slots. You can do more tracks per Play VSTi, I think I can run up to 16? with the libraries I use? I split them up to keep things organized, I could run them all out of one Play VSTi if I wanted too.
If you are talking about more than one MIDI track into an Audio track, then you need to look into using Group tracks.
Hope this helps