To the OP, I didn't see where you have described an analog rig that you're trying to capture... so I'm going to assume that you're looking to find your sound with the KPA, and that's a really tall order.
It's plug-and-play in the sense that you can plug in and try thousands of possible amps through thousands of possible cabs and mic combinations - but that's a bit overwhelming to just about anyone.
The fact that you're going into a guitar cab is a plus, it removes the speaker cab/mic from the equation. At this point, just find an amp that sounds good to you... find the amp that is the closest to what you want to hear coming out of your cabinet. I don't envy that task, it'll take a long time as there are thousands now on the Rig Exchange and in the packs, but you'll learn how to whittle them down fairly quickly.
If you know what type of amp you want, then find those first. Holdsworth used a Mesa/Boogie studio preamp if I'm not mistaken, so look for something in the Mesa Mark family (studio preamp, quad preamp, Mark I,II,III,IV, or V) and that might get what you're looking for.
Also, to use it with a guitar cab for best results, stick to Direct or Merged profiles so that you can disable the cab on your feed to the guitar cab. On studio profiles you might have good luck doing that, but in my experience not usually.