With a given motor & prop combination, I doubt you'd be able to use both 2S and 3S packs. If it flies well with 3S packs, it will probably be severely underpowered with a 2S pack. If it flies well with a 2S pack, you will probably fry the motor, ESC, and/or battery with the 3S pack. If you change props to optimize the current & power for the 2S and 3S packs, then you can probably do either.

As far as whether that ESC can work down to 2S, you'll have to ask Horizon/PZ. I don't know where you can find a manual for it, and I believe the label just says 3S.

The AR6110 is a short range park flyer receiver, so if you are putting it in a small park flyer that won't get flown out very far, your set. If it's a sail plane, or plane large enough to fly out very far, you should consider using the full range AR500.