[popcornmix]

Using dvdplayer plays the DivX 3 files! Is it possible to specify a different default player depending on the file? Either way, this saves me from converting DivX 3 files.

Unfortunately xbmc doesn't allow that degree of control (if it were just looking at the file extension, it would be easier, but you do have to open the player to parse the file to make this decision).
There is a long term plan to merge omxplayer and dvdplayer, which may make automatic switching like this possible, but that won't happen for a long time and will involve refactoring a lot of dvdplayer code which may be hard to get accepted.