the only strategy possible to get midi files into other formats is to actually record them as they are playing back. Any software that claims to do midi -> wav conversion uses this exact technique.
Download record pad here: www.nch.com.au/recordpad
And set the recording channel to "Stereo Out Mix" or "Wave Out Mix" or something with a name similar to that (the name changes from sound card to sound card). Then hit the record button, and start playing your midi file.