Hi,
I took a look at the Disk I/O and nothing related to the PPCS6 muxing process seems to show up there.
Attached is a screenshot of the Disk I/O window and the PPCS6 export window with the process info.
Also, I found a thread where they mention a similar problem in Adobe Media Encoder. At the end of the thread they mention a codec called handbreak, which they say is better than Main Concept and doesn't crash during export.
http://forums.adobe.com/message/5133148
What do you think?