From my experience, I've not seen any .XA files on Saturn games, however, I have seen .DA files IIRC, and they correspond to the CDDA tracks in certain games. Their filesizes are really big and if you try to extract them from an ISO or the game CD itself, you'll run into read errors because they're sort of like dummy files pointing to the CDDA tracks.
This makes me wonder what type of data are inside the MODE2/2352 tracks on games that have dual data tracks.