Well, my S975 has been in the house for 2 days now and I must say I think Yamaha might have missed the boat on this one. There are several issues which have been posted about on both this forum and the UK forum which so far Yamaha has not addressed with an OS update.
1. Volume levels are very inconsistent between styles
2. Volume balance between the style and RH voices is very inconsistent.
This is a big issue which has not been present on any of my previous Yamaha keyboards including PSR3000, T3, T4, T5, Genos, and S950. Mostly you could take them out of the box and go play a gig if you wanted. Not true of the S975.
Also, not much change to styles from these other keyboards and frankly, not many new styles that fit older music. On the positive side most all of my PSR3000, and T3 styles play nicely. T4, T5, Genos styles all need re-voicing for for all four variations to work well. S970 styles work for the most part but not all.
Anyway, this is my findings for now. I'll add more later.
Deane