Peter123 has posted a review of the A2S IEM on Head-Fi. It is a hybrid single BA with a 10mm dynamic driver. Included in the review are a few comparisons with other Chinese IEMs including the original A2 (which I own and use frequently). From the review it appears that the A2S is a marked improvement over the original A2, especially in the mids.
Pros: Excellent build quality, easy to drive and fit, non-fatigueing and easy to enjoy siganture
Cons: Slightly soft bass, not the greatest soundstage width