Why don't you send me an email and let me know what's going on with your DVD Changer? The problem with those changes is that your not always going to have the same timing every time you press the same exact command. A lot of variables come into play:

1) Location of changer at the current moment
2) What the changer is doing when you initiated the command
3) How many discs you have in the changer
4) Age of the changer
5) RF gain
6) Interference or emitter placement

Sometimes you have to sacrifice speed for accuracy...