Knuckle Head is "a bad boy bruiser with a sweet and soft side that it's not afraid to show". It is capable of tones that range from sweet, glistening cleans to SRV and Yardbirds style smokin' hot crunch right through to punishing high gain destruction, according to AcmeBarGig.
Here's what Ken has to say about Knuckle Head: "Knuckle head is the brute force amp of the collection. His poweramp is the main tone maker, it gives you a raunchy heavy distortion or a nice crunchy yardbirds type tone. Although it is capable of all the sounds in between. I have only ever been able to get this distorted sound from a real amp and no other amp sim has ever been abe to give me the raunchy sort of distorted high mid that this one does. With mid cranked, Treble master cranked, bass 3/4, Treble off, master 1/4 everything else cranked, it will give you a superb machine gun type of fast picking while riding a string, like picking the e string really fast while palm muting."
Bear in mind the Preampus Line amps are Head ONLY so you will need to use some external cabinet modeling.