Below is how to grab a handle to an open instance of STK or how to create an instance of STK through Matlabs Actxserver functionality.
%if STK is not open..
%start it all off - create COM object
STK = actxserver('STK8.application');
%if STK is open...
STK = actxGetRunningServer('STK8.application');
%get the object model root
root = STK.Personality2;