Shink,
I remember the trouble I had choosing a new arranger when it was time to upgrade my setup from the PSR740 - MZ2000. I ultimately chose the PA80, but looking back, I could have easily chosen the PSR9000 as well.
There is a good deal of user support and styles available for the PA80. The same is true ( and maybe to an even greater extent ) with the Yamaha arrangers. As for the Ketron stuff, I am not sure how much there is in the way of extra stuff. I do know that Ketron AJ provides excellent support for the baords and he posts here regularly. He provides one on one support in a much more personalized and personable manner than I have seen from either Korg or Yamaha reps.
These are not easy choices. All seem to be very good ( I say seem because I have no "hands on" with the Ketron stuff ). I can only tell you why I chose the PA80, and my criteria is different from a lot of other players. Ichose the PA80 because I felt it was more like a workstation / arranger hybrid than any of the other models at the time. It offers full voice patch editing on par with any good workstation, along with full access to the raw samples. I also liked the way the styles sounded. Since this was on top of my list, I was able to overlook what I felt was it's biggest weakness.. only two fills per style. That most of the style variations contain "mini " fills at the 4th or 8th measure of the loop also helped me ooverlook the "fill" flaw.
The primary reason I did not consider ketron was because I couldn;t find one anywhere near me to demo at the time. From the demo's and MP3 files I've heard from other users, the SD1 and the XD9 sound fantastic. I would need to delve into a board a little though before spending the big bucks, and at the time it wasn't possible for me to do so. Korg, Yamaha , Ketron, Roland, .. all good but.... Try before I buy is always the number one priority for me.
AJ
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AJ