I did look into this.
Unfortunately, it seems the source code has passed on with the sands of time (for whatever reason) and is no longer available.
Sorry... Seems like it was such a simple thing, but I suspect that, as Team Xecuter uses some ancient sources to build their BIOS, the same might be true of their DVDX app (using an ancient build of the XDK, that supports MPEG2/DVD playback) - so it's probably not buildable these days, anyway, unless the old libs and headers could be grabbed.