As many of you may recall, I was in love with the PA3x .. all except for the lack of speakers. I think is was cosmetically, my favorite layout and great key feel, screen placement etc was a perfect fit for me. The 900 feels about 80-90% the same as the 3x .... just a tad lighter, if anything, but not much. All the essentials are in the 900, but if you had to miss something:
1) mic input (XLR) and better harmonizer
2) sliders
3) multi outs for better mixing
4) more mastering choices

For the way I use a KB, the 900 is better suited, as the speakers become as important as a band member to me when I am in tight spaces (which is ALOT). Don would make a 900 sing, and he'd be comfy the first night on it.