I sell the Yamaha PSRE403 and am very familiar with it. It is the lowest priced Yamaha with the "sweet" voices and so I would say it stacks up with many of the sounds in more expensive keyboards. It has the knobs to control filters, envelopes and even has a built in arpegiator. It's acoustic sounds are in my opinion better than what you would have had in the older SY keyboards from Yamaha, but don't expect the synth type sounds to be as powerful. The PSR's do acoustic sounds as their primary voices and although the synth sounds are good, you don't have as much manipulation as a dedicated synth.
For the money ($229.00 in the USA including the survival kit (AC, Headphones, Sustain pedal, 2 year warranty, DVD software for computer) it's a real bargain.
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George Kaye
Kaye's Music Scene
Reseda, California
818-881-5566
www.kayesmusicscene.com