when it comes about outputs, for sure more means better if you are in the studio work.
if you are performing live, probably you don t need more than 2 outs (R,L).
i believe korg delivers a good quality outputs, probably better than psr 1500, but anyway, you dont have to worry too much about this. i rarely have heard about someone having problems in this area.
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Yamaha S770, Studio One 3, EMU 0404USB, ESI, ATH, Dell. And others.