Hi Pepe,
I'll switch to english here, as I only answer in spanish on the KVCD spanish forum.
The problem is really the Apex models. I know that they all play correctly at 29.97fps, but only some models play at 23.976. What you might want to try is encoding with the KVCD LBR as MPEG-2, at 23.976fps with 3:2 pull down. I believe the Apex models do like that. So then you'll be able to play your video smoothly. If you're doing your captures at standard 29.97fps, and your original captures are FILM, then you must Inverse Telecine your material in order to encode at 23.976.
-kwag