There are several reasons why the PSR-9000 and 9000 Pro's polyphony can at times be problematic:

1. Many of the sounds on the 9K and 9K Pro are stacked with up to 4 layers. Dependent upon how many sounds are layered your polyphony could be cut by as much as four times. A four layer sound would give you around 32 notes of polyphony.

2. Some of the sounds on the 9000 and 9000 Pro are in fact not "true stereo" but mono sounds stacked then panned hard left and right to mimic stereo. This effectively reduces your polyphony in half. Use several of these "stereo" sounds in a song and chances are you will run out of polyphony very quickly.

3. Earlier versions of the 9K and 9K Pro had software bugs that caused unnatural sounding drop outs when excessive polyphony was used. Thankfully Version 2.0 and version 3.0 fixed most of these problems.

4. The 9K and 9K Pro had bugs in earlier software that also caused drop outs if an excessive number of sounds were used (even if the maximum polyphony wasn't exceeded). I'm not sure if the newest software Rev fixed these problems or not.

Yamaha, not unlike most manufacturers, hypes the number of voices and amount of polyphony as a selling feature but deliberately fails to mention the fact that their instruments can't truly produce 126 or 128 voices at once. Oh sure you could probably get close if you didn't stack the sounds but then the keyboard would sound like crap.

One case in point would be the Yamaha CVP-209. The CVP-209 is touted as having 256 notes of polyphony which is somewhat true. The CVP actually uses two sound engines, one for the piano and "Natural" sounds and one for all other sounds (Cool, Live, Sweet, etc.). Each processor has 128 notes of polyphony but that polyphony can't be shared amongst one another. If they could be shared it would be very difficult to run out of polyphony but anyone who's played a CVP-209 and held the sustain pedal down just to see what happens, will quickly realize the CVP can and will rob notes. The only way around this would be to design a newer, faster processor that could handle all 256 notes of DATA. This no doubt would raise the price of the already heavily inflated CVP series likely pricing it out of production.

When buying any synthesizer, keyboard, or arranger, buy it for what it will do at that time, not what it is supposed to do in a future software upgrade. Also, be certain that the unit can in fact do every function the manufacturer states because chances are it can't. Its called creative marketing and manufacturers know just how to word an ad so you want their new products.