Roy,
Both the S2 and S3 have poly AT. The S2 is 61 key, the S3 72 key. btw- I have sold my S3 awhile ago, had regrets and bought an S2. Once I found a Kurzweil MidiBoard in mint condition, I sold the S2. I know of an S3 in Oakland, CA that may be for sale. I also have an extra Kurzweil MidiBoard (I know, sounds crazy!) that is in fair cosmetic and good working condition that I would like to sell.....