I ended up changing my approach to the problem. I used the RTTTL format because it fulfills all my requirements. The format is limited to playing only one note at a time. That means chords (two or more notes &| string played simultaneously) aren't possible. I have only been testing the RTTTL conversion method for a short time so I could be wrong, but I couldn't find any way to accomplish chords with this protocol.
Since my program doesn't require that more than one note be played at the same time, I didn't end up sacrificing anything by using the RTTTL format.
I would still like to figure out ANY way to programmatically convert tablature in any type of structured text form into any type of audible file (MIDI, WAV, MP3, OGG, WMA, etc...)
For now, I'm closing this question because I've resolved my issue although not exactly the way I initially intended on doing so.