Darwin Streaming Server 6.0.3 won't send Closed Caption track
I have no direct experience with DSS, but it appears, from what I could find online, that DSS does not support streaming a text track.  Rather, you seem to need to reference a non-streamed version that has text data.  I unfortunately couldn't find much more on what the one place I found mentioning that intended, so I'm sorry that it isn't very clear, but it was the best I could find.

Hopefully someone else has actual experience with DSS and can provide better guidance than I.