Nardoni,
it's definitely not the eq. The 3000 sounds very similar to my psr640 in terms of basic sound quality (not actual voices etc.). And even when I eq my 640 on my mixer it doesn't sound as nice as the Tyros. Maybe it has to do with the DSP system on the Tyros (somebody mentioned that here), but the Tyros definitely has a better sound system. The eq only brings out or reduces certain frequencies, it cannot actually improve sound quality that didn't exist to begin with.
Zalmi