Esh, great playing, thanks for the demo.
Chris - I can see what you mean about the SG-1D. I still have my original Korg SG-1 (76 key version) I bought in 1986 and can tell you that it weighs 30kg (65lbs)

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From memory the Korg SG series has 12-bit linear PCM samples which gave it a certain bright presence at the expense of some smoothness. At the time the SG-1 certainly managed to cut through on stage when playing in a live band.
The thought of comparison with the SG-1D could be due to the relatively low bit rate of the demo (89kb/s). To my ears low resolution mp3's have a habit of sounding like low bit-rate samples.
It's likely that the ES4 (although never having played one in person) would sound much fuller/ richer/ smoother than the mp3 allows.
Esh, please correct me if I am wrong.
Kind regards,
Mark