MediaShout for Mac and Slideshows
MediaShout for Mac supports either PowerPoint for Mac (2008 only) or Keynote 5 (iWork '09). When playing a slideshow, the slideshow command should start PowerPoint or Keynote if they aren't already open, but it's recommended for them to be open and configured to present on the correct displays beforehand. MediaShout for Mac can't configure the presentation settings for these apps, so if they aren't set to present on the main display, they won't.
Basically, when you play a slideshow command, MediaShout opens Keynote or PPT (depending on which type of file you assigned to the command), opens the assigned file in that application, and plays the first or designated-first slide onto the main display. The KN or PPT application itself will open onto your control display, over the top of the MediaShout app window. Use the KN or PPT application to play and otherwise control the remainder of the slideshow.
When you advance past the last slide in the KN or PPT slideshow, MediaShout's app window will reappear on the control display, and the next cue below the slideshow command's cue will play to the main display. At this point the slideshow command is done, so all control is returned to MediaShout.
NOTE: When playing a slideshow, the Countdown Clock & Key Text feature is not available and cannot be controlled. This is because MediaShout has to open the slideshow app (i.e. Keynote/PPT) in order to play the slideshow.