I needed to lighten my load, since I had chronic lower back pain, and chose the Pa900; my pain has largely gone!

Note that thePa900 has the voice processor which the Pa600 does not. I love the Korg songbook and custom list features for what I do, and I think the internal speakers are excellent (I think they are a notch up on the Pa600 but check with Tony). In smaller rooms it really is all you need. In larger settings I supplement it with an additional speaker.