NUMPAD NUMPAD NUMPAD! I hate selecting sounds on the s-900.
First, pick a category, which is one set of buttons, then, select which page of sounds, which is another set of buttons, then, select which sound on that page, which is yet a 3rd set of buttons. Makes me crazy. Same with the styles. Wish there was a numpad like my XP-80 has and everything is nice and handy using only 1 set of buttons which is as handy and familiar as a calclulator or phone.
Then, I want nord's piano, E-piano, and organ sounds. Yamaha's Super articulation sounds, Roland's SRX-01 drums. And the basses from the SRJV expansion board, and the banjos, dobros, and steel guitars from the SRJV country board. Korg's styles, but Ketron's latin styles. That would be a good start.