I don't think System thing is anything to do with it.
Make sure the MIDI tab is selected in the Inspector.
Click on the "C" under the FX bin and choose which channel of the TTS-1 you want that track to access.
Alter the sound in TTS-1 by left clicking on the part's name (Piano1, by default, on all tracks) and choosing your sound from Presets, wind, etc.
If you want to use another sound, insert a MIDI track, select TTS-1 as output at the bottom, click on "C" again and choose another TTS-1 channel, and so on.
I hope that helps.
It's been a long time since I've used TTS-1, so I may not be 100 per cent right.
Shout back how you get on, or PM me if I can help more.
Oh, and don't expect the brass to sound like "The Phoenix Horns" or "Birth of the Cool".