If you're trying to decide between the S-500 and PSR-1500 I'd take the 1500 hands down. Granted it's a little more expensive, but you get quite a bit more with the PSR-1500. One obvious plus for the 1500 when compared to the S-500 is poly. The 1500 has more than twice the poly of the S-500 along with many other advantages.
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GEAR: Yamaha MOXF-6, Casio MZX-500, Roland Juno-Di, M-Audio Venom, Roland RS-70, Yamaha PSR S700, M-Audio Axiom Pro-61 (Midi Controller). SOFTWARE: Mixcraft-7, PowerTracks Pro Audio 2013, Beat Thang Virtual, Dimension Le.