Hi,
Soundwise it is hard to beat BiaB, because all the licks are played on real instruments by live musicians, but the SX970 offers more flexibility because you can play the chords on the fly.
Two very different bests IMHO.
N.B.: Woody Piano Shack made an extensive video comparing BiaB with the PSR SX900. Here it is:
https://youtu.be/cK8p1p2KLmQEnjoy,
Vinciane