Hi Spalding
Yes you can change the Acoustic Bass of a Korg style (Or any normal voice) with a better quality Acoustic Bass voice from a VSTi, however you can’t just substitute and ordinary Acoustic Bass (No matter how high the quality) for a Mega Voice Acoustic Bass, as the voice you choose has to have a similar set-up to the Mega Voice.

Most people think Mega Voices are just ordinary voices with a few extras added, however they are NOT, they are specifically engineered for style play on Yamaha instruments. (This is why (Just like SA Voices) you don’t see many Mega Voices released, whereas ordinary voices are aplenty)

Bill