Timidity works very well indeed. I've successfully converted lots of MODs without having to use any special settings, but I think there's a problem with stereo, which I think is limited to S3M files. If you
convert an S3M to an AIFF you'll find that a centrally-positioned 'solo' instrument ends up on the left hand-side in the AIFF and (if my ears serve me well) what's in the centre ends up on the right.
In other files the sounds on the right also end up on the left. Most odd! Anyone else have this problem?