Acronyms, acronyms, what's a boy to do?
Don't assume that, just because another manufacturer uses a two letter acronym for some unspecified improvements to their voice technology that it has ANYTHING to do with another's.
Yamaha's SA technology is the ONLY hardware system that is capable of detecting legato and staccato play IN REALTIME, and use that to determine which set of samples to trigger. Plus, it can modify that behavior based on other rules as well, such as intervalic rules (don't make a squeak until the interval jumps more than a 4th, for instance).
Now, this isn't groundbreaking stuff, many software sample players have had complex rules-based behavior for several years. But it is, AFAIK, the only HARDWARE, non-computer-based (in other words, short of Neko, Muse or possibly MS) arranger that can do this. From what I can glean from Korg's literature, the RX technology simply uses more velocity layers to get different sounds, but you can't apply intervalic and legato/staccato rules.
This truly is, I believe, the only real improvement to ROM-plers in the last ten years. More RAM and more velocity layers is just more of the same. But the ability to play a natural technique, and have the instrument figure out, fast as a blink, which of a totally different set of samples to trigger to make the samples have that exact same natural technique is a totally new concept for hardware.
And going by the mistakes that Yamaha's WS division have made, trying to port this over to their side of the company, it is obvious that some of you are not the only ones to fail to grasp the overall concept..! The T2 has done an amazing job of making all this formidable power completely transparent to the user, whereas the MotifXS still demands a lot of non-musical (button switching, pedal pressing) techniques to achieve the same thing.
Now, this is NOT to say that any Joe Blow can sit down at an SA voice, and immediately get the best out of it. First of all, it requires a VERY refined legato/staccato technique, similar to the technique you would use on a Minimoog to trigger the envelope sweeps EXACTLY where you wanted them, and no other place EVER. That takes a degree of control and practice few attempt (not really needed for many other sounds). THEN you have to learn the intervallic rules for each sound, and play with those in mind. And each sound has a different one...
So it's unsurprising that some don't get it (you might have to actually KEEP your arranger more than a couple of months to get the hang of it!) and some do. There are some completely believable demos posted at Yamaha that showcase exactly HOW realistic these things can sound. What's that? You say YOU can't make it do this? They are playing the exact same arranger and sound as you. If you can't get it that good, just exactly who is to blame..? Oh, that's right... It MUST be the arranger!