Umm, from the signature, it looks like you play guitar.
Why not just record your own parts, or use realtracks?

One way to help the midi sounds is to run them thru a guitar processing effect; it helps add to the illusion, espcially electric guitar sounds.

As PGFantastic alluded to, the way the midi track is played has a lot to do with it too. If the track is recorded by a piano player pounding out chords, it will not sound like a guitar just by changing the sound. Think about the mechanics of how a guitar creates sound - the strings are strummed in either direction, so it helps if the midi track is laid out that way... there is a lot to consider besides just the tones used. A finger squeek here and there also adds to the illusion..

Getting into soundfonts will give you a lot of free choices to experiment with.
I created a nylon gtr soundfont a while back that a few people really liked, and I have found others that I liked more.

I do not work here, but the benefits are still awesome
Make your sound your own!