Hi Spalding
The new upgraded RX technology and memory goes way beyond SA, and is akin to EA (Extended Articulation) that Yamaha now use in their Motif range of instruments.
SA was good in its day but technology moves on (As is demonstrated with Yamahas Motif EA voices) and so now manufactures do not have to limit the articulations to a simple Mono/Poly (Solo/Legato) of SA.
I will see if I have time to put together a fuller explanation when I get back from work tonight.
Hope this helps for now

Bill