I just conducted a test. I had a high bitrate H.264 Quicktime file of some footage I had edited from AVCHD. I did an AMA link to the file to bring the file into MC6. I imported a random closed caption .aaf file that had been created by MacCaption and put it on the timeline with the linked video. Here comes the cool part.
I exported the sequence to an MXF Op1a file using the XDCam 25Mbps compressor. Transferred the file into our Omneon HD video server and played out the file with captions.
Very nice. Now I can export directly from my AVID systems into my HD playout server.
Another useful one that you don't read about in the marketing materials is the ability to export ISO audio tracks now in QT and BWF. The next step would be to insert the track name (if entered) into the export files itself; for example the track info in the BEXT chunk of the BWF file. Would be great for deliverables such as 5.1 etc. Right now I do that my opening the BEF file in WaveAgent by Sound Devices and entering it there, but it could be done all in one step.