These sound quite good!
As do some piano and strings demos.
Comparing it with a Casio is an insult. I think Roland put in very mixed quality here, and as they squeezed in such a vast number of sounds, they obviously chose to compress some of them like brass, but not all.
I guess all in all it is better and more versatile than the BK-5 (and it costs much more than the BK-5), but as I said you can't compare it with the BK-9.