I would like to copy a DTS track from a DVD to DTS CD.

The thing I should do is get the ac3 files, and then convert them to DTS wav files. But how can I do that ?

The first thing is that I can't extract ac3 files (flaskMpeg only reports video tracks...)
Secondly, I saw a software call SurCode DTS (to convert from ac3 to wav) but it is not free.

Did someone already do that kind of thing ?

http://doom9.org/BeSure.html

I just saw that this morning. I have to try that, but it seems that it uses SurCode DTS...

There are no freeware DTS encoders, so yes it uses Surcode.