Sorry but I don't agree about the nylon guitar. Yamaha has pretty much overcome this, however they are still dilligently working on the picking envelope of the overdriven electric. If all you have is GM, then that is why. To my ears, most of the timbres created in general MIDI are just that; General, and not specific. The sounds are out there, but unfortunately similar to many things in life....you want, you pay.
MORPH!