All except for splicing into the AC3 track. Unless there's software to do otherwise, I would think the whole soundtrack would have to be recompiled. That's why I like using Vegas - it's so easy to mix and match footage and audio. You can slide it back and forth, resize it, and speed it up/down until everything is a perfect match.

Of course, like Combustion, such features take a lot of practice to perfect. I went through several trials with Combustion before figuring out a streamlined way to create the opening crawl to match the EOD Documentary. The programs are very powerful, but you really need to get into the guts of the things to make them do those special tricks.

BTW, did you ever get the Combustion help file and the link to the Vegas sample projects?