Do SD2 styles sound just as good on an Audya as thye do on the SD2,
It will sound exactly like all previous Ketrons SD keyboards. As for the Audya, many of the sounds will be the same, but not all.
It's a module of the SD series keyboards with additional content.
or do they require a lot of tweaking?
There is very likely no tweaking for all SD series styles, and little tweaking for Audya styles.
Regards
James