The best thing about the PSR-SX900 and ANY Yamaha MOTL or TOTL arranger, is their highly refined Style File Format (SFF). Also, the huge library of styles that are available. But as a less-skilled player, I would probably use the SX900 in a two-board setup, driven by MIDI notes coming from... a Roland! (see my other post here):
http://www.synthzone.com/forum/ubbthreads.php/topics/502636#Post502636

Since the original Tyros, Yamaha's premier chord recognition mode is called "AI Fingered." Some less-skilled players including me find it frustrating, because pressing a single key triggers a unison [1+8], instead of the more common and expected major chord. This makes fast progressions more difficult to play relative to other brands. A minimum of two fingers (in root position) are required for major chords; this sometimes necessitates repositioning the whole hand to reach the third above. In other cases, a minimum of three keys must be pressed to avoid triggering an "on bass" chord, because bass inversion is an implicit behavior instead of an independently-controlled function (as on Roland, Korg, Ketron.)

At the very least, there should be a menu option that allows single notes to be acknowledged as major chords (i.e., instead of unison.) Making this a user option would leave no one worse off. The SX900 has some other modes that allow one-finger majors, but these modes have other serious limitations. And ALL modes occasionally require pressing keys that aren't actually part of the chord, to trigger the desired behavior. After years of testing and playing my favorite scores back to back on Roland and Yamaha arrangers, I've concluded that Roland has easier, more convenient chord recognition for my playing style and the types of music I like to play.

In almost every respect the SX900 is a great board. But chord fingering is hugely important! Until Yamaha implements Roland's chord recognition modes, there will always be a Roland in my stable. Ironically, many years ago Roland released a firmware update to incorporate Yamaha's simplified chord recognition as an optional mode in the menus. So why doesn't Yamaha reciprocate?? It would make it easier for Roland players to transition from what now looks to be a defunct brand, and may even result in "conquest" sales! My $.02.