The reason Yamaha Mega Voices are so good is because they are Midi loops that have been recorded using a Midi controller suitable for the instrument, (Guitar Mega voice = Guitar controller) with additional effects controllable by velocity and out of range notes.
This is also why style conversion software cannot make a good conversion with a Mega voice style to any other keyboard.
The only way to get a Mega voice style to sound even better is to play it on a Wersi with the OAA (Open Art Arranger) software, which allows the sounds to come alive without the compression effects of the Yamaha sound system.

Bill