The interwebz says AC3 support was removed from the Sandisk app arsenal some time (not too long?) ago, but the workaround is to Open in Infuse…
So I bought an ixpand 3.0 recently, but when I try ‘Open In…’ (with any movie file), Infuse (and VLC) open as expected and the movie starts playing…for around 5 seconds every time. Then playback stops and goes back to the VLC/Infuse home screen.
I thought it might be an issue with space on my iPad, but the free space was almost double the size of the video file in most cases.