Hi six channel,
I'm a RB user and an occasional forum visitor, which is why I'm putting in my twopence worth so long after the issue was first raised: I don't know anything about supertracks but I do from time to time play (or write in the piano roll window) MIDI stuff into RB and find the track is silent when I first try to play it. From memory, there's a signal showing on the relevant track in the tracks window but no sound.
What works for me to kick it into gear is simply to duplicate my non-sounding track(first command in the "Track" menu in the top toolbar)onto the next available track, and it works!
That is, both original and duplicate, together or seperately. I can then delete one or the other and the remaining one works fine.
I'm aware this method sounds more like voodoo than soundly based technical information and I'm glad that you've received plenty of the latter in previous posts, and also that your problem may have had different causes than mine and require a different fix. Nevertheless it's a quick and painless thing to try and just might work for you and anyone else in a bind like this.
Clinton.