Mr9000...simply mathematics to start..The 9000 uses mostly 4 voices[polyphony]to produce a single tone, as the G1000 uses mostly a single voice to make a tone[sometimes two]...So on a common tone, the Roland [G1000]will have a 64 voice[polyphony] tone, where the same sound on the 9000 will be reduced to 32...

The same with the Korg , they use 1 and 2 voices to make a tone..

But more important than this....is allocation..

I played the 9000 and absolutely run out of voices...I am sure other 9000 owners will attest to this..Esch,Pesce,Boyd[I am being formal]..].