I think Microsift GM (general Midi) plays back/maps through the onboard sound card...?....and thus you hear playback of midi ok..as this is the default player?...perhaps? Win 8....I do not know for sure...But in my case, Selecting the audio device I want all tracks to play through even midi...to my Audio device of choice, This has to be default playback for me set as Allen and Health r16 ...in win 7.
So not sure if this is any help...Just it works for me...and so I assume it may be likewise for you?
When installing new drivers and updating ...things can be reset...Just trying to help....
Sir Les.