Playback problem with MS4

I have just upgraded to MS4 and I think I have sorted most of the features that I am trying to use, however.....
In MS3.6 When I play back a score, I can display on the screen just the part I am interested in and, via the mixer, play just this part or all instruments in the score. I have yet to discover how to achieve this in MS4. Any guidance will be most welcome. Am I missing something obvious?
Thank you
Andrew