Don't know about a Mac and I have never done it myself, but I am almost certain that eac3to can do it on a PC. You would need to have Surcode (or whatever) installed. If I were in your situation I would go to AC-3 5.1 at 640kbps: it has always sounded good enough to me, so I have never felt the need to invest in a DTS encoder. I understand that you want DTS though, and it should be possible.
23.976 to 25fps? Why would you want to turn gold into lead? (kidding) :-D