I've been told I should post this on the forum, just in case someone else runs into the same problem...
So I've tried to get smplayer (0.6.9) working with mplayer2 (2.0rc2). It was complaining about subtitles, and switching between the old subtitle method (-noass) and the new one (-ass) didn't help. In any case, unticking the freetype support in the main subtitle tab works, and now I can use those two together.