I have it side by side with PA4X, PSRS950 and EA7. The x900 sounds great, as do the Korg and Roland. They all have a different "personality".
It blows the S950 away in all categories, sounds, drums, styles, functions.
Drums are MUCH better, styles are much better, many of the old styles are revoiced and rebalanced. New country and R&B styles are great. Guitars are great, especially the Pedal Steels. The OOHs and AAHs are very well done, better than Korg and Roland. New Cajun accordion is authentic. Most sound insert effects are great.
I can't see giving up the EA7 because it is a good arranger and very portable. However I am now entertaining the thought of adding the SX900. Seriously.
It is really deep and there is a learning curve, even though I am very familiar with operating previous Yamahas. Too much to get into right now...I'm still learning lots of new features.
I haven't run it into my Big PA system, just a small one at the house, but if the VH isn't satisfactory, I already have Harmony M's in both my setups.
Oh, and the built-in speakers are by far the best I've heard in an arranger.
Negatives: (they all have some). USB ports poorly located...no lettering on the top of the keyboard to indicate where to plug connections in...no VH on/off indicator...Leslie on/off needs work, but the switch can be re-programmed for other functions...only two pedal inserts. Organs are the weakest sounds on the 900, of course in my opinion, as all of this is.
I'm sure there are more, but I'm still experimenting.
If I do get one of my own, I think I'll start completely over on Registrations.. Either that or go through each one individually to see if the new styles and sounds are better than what I have saved. In almost every case they are, even though my S970 registrations work fine as they are. Why make your new arranger sound like the old one?