If you want authentic sounding guitars and basses in a midi synth, then be sure to check out Yamaha's "Mega Voices" on their latest keyboards. You should be able to find a video or two of them on YouTube as well.

There is also a software program they use to convert a standard midi guitar file into one that utilizes their mega voices. The software adds the slides, pick sounds, mutes etc that a real guitar has in midi format.

Trax