Since you left out a lot of important detail, I'm not sure exactly what you've done, but I've got the jist of it.
If you've actually recorded the MIDI information file (.mid) to a disc and play the MIDI file on a computer or other MIDI capable device, it will play the default MIDI instrument (#1) which is an "acoustic grand piano". To get it to play any of the other general MIDI instruments, you would need to choose an different MIDI instrument in the MIDI synthesizer (usually a sound card) on your computer.
In Music Maker, you must choose the MIDI instrument you want played. Then, you would EXPORT the MIDI file (or the entire arrangement) into an audio format from the arranger. This will give you an audio file (MP3, wav, etc.) of the MIDI sequence using the instrument you chose. If you export a MIDI file from within VITA, it will be exported as a MIDI file only.