Is there a website I should go to or does anyone know the best settings for this amp If I want to play nirvana.
Here's how I have mine(on one of my custom channels)

Gain @ 6
Treble 8-9
Middle 10
bass 3

Also on my EQ pedal i have it with the middle cranked and the bass and treble frequencies up a little bit too.

Then do what ever you like with the effects
Keeping it real since '92