Welcome to the forum bb013,
AC3 and DTS are just different audio formats. The /2 and /6 are the number of channels. In theory DTS has a better dynamic range (the diff between the loudests louds and the softest sound), however it uses up more MB of space than AC3. Also you need a DTS decoder card to play DTS format audio , so unless you have a A/V receiver that does this > then no sound .
Unless you are a high end audiophile I recommend checking the AC3 / 6 and AC3 / 2 boxes in Clonedvd2 and you'll save more room for video quality and the sound will be just fine. Uncheck the DTS / 6. the reason you need to check both ac3 /6 and /2 is the 2 channel is used for the extras...you know the directer's comments etc. so if you leave that off, your special features might be missing the audio.