While you probably could use an amplifier like this for guitar, you usually wouldn't want to unless it's being used for acoustic guitar or vocals. The reason being, an electric guitar amplifier is going to add a lot of character to the guitar tone that you actually would want, where as an amplifier like this is going to strive for a perfect clean reproduction of the original audio. This is why a lot of guitar players prefer to use old tube-based amps, they add a lot of character to the sound through the preamps and power amps that match what you hear on the recordings of your favorite artists and sound great (though, some argue today solid-state modeling amps sound just as good). With that said, there are a lot of projects and schematics on the web which try to recreate some of the popular guitar amps like the Vox AC30 and Fender Twin Reverb, which would be fun to try and build.
Now if you wanted to make a PA system, I don't see why you couldn't use an amplifier like this with some modifications.