Curious, I've never heard large strings of that quality in a Tyros demo before. They sound like a high-quality string library like the DSF strings for Motif or at least like Roland SRX 04. I'm a bit confused, going to test the S970 myself some time to verify this.
All the sounds of the s970 are also in the Tyros 5 as well as the CVP709
I think what makes it special is the composition, its a sequencer file. Using several string sounds at the same time..