As with most state of the art rigs in this field, the M1 has not aged well. Though the Kawai K4 I got in 1990 was a compromise because I couldn't afford the M1, I find myself missing the sounds on the long since hocked Kawai--they were on the whole much warmer and more expressive. Still, I've only used the factory presets so far. I have no doubt that third- party programmers have much better sounds to offer. And if I can ever get my hands on a manual*, I'm sure the sequencer will be a great utility *hint hint. I found this site in my ongoing search to find M1 docs. Feel free to help in any way possible (or at least in any way reasonable. TIA)
Synthsite Comment: There's a few 'classic' sounds' that still get used for remixes, most notably the Perc Organ 1 (A lot of NY house), Pick Bass (En Vogue) and the ubiquitous M1 Piano.
Comments About the Sounds:
Classic but a bit dated..
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Rec'Up A lot of public domain banks and organized libraries (thousands of sorted out and classified sounds) you can download for free. You'll find too totally new and unpublished banks.