MMlite card is needed to play enhanced sounds on an s2000, it's what holds the sound simm.
The other terms are dealer specific, but most S2000's that have the "ears" are stereo sound with a low range speaker as well in the coin tray area. If you add the mmlite board and the correct simm for whatever slot theme you have, it would be considered the best you can get with the slot. I would also ask to see if they can use the enhanced stepper board (127x series) instead of the older 50x series, as the older series have a noise through their sound amp, the newer enhanced boards are absolutely crystal clear with no noise.
The other thing that just came to mind is the short reel glass (printer next to reels) and long reel glass question if you are getting a 3 reel slot. If you are getting a 5 reel slot, they are all long glass (with printer on topbox). The short reel glass slot is difficult to convert from a 3 reel to a 5 reel without making some cabinet mods. The long 3 reel glass machine is easy to convert to 5 reels. Just something to keep in mind if you ever want to do that in the future.