There is a workaround to this problem that I found, which is to simply add the TTS-1 instrument to the project and now all the midi tracks point to the TTS-1 and the TTS-1 points to Master. The only drawback is that the general midi instruments are not labelled with their common names, only numbers, so you need a reference chart if you don't know them by heart. If you don't want your TTS-1 on top, then you could select all the instrument tracks first, label them and then add TTS-1 before starting to add your midi information to each track.