it's no one thing, its all the great people here giving tips.
the forum is my single best source of learning and the people who makes videos, blogs, etc about tweaks.
the other thing is to remember there are no rules.
its like music theory, its not right/wrong, its just a well understood way of achieving expected outcomes for people with a built in preference.
since we aren't really messing with voltages, resistors, etc only using them as a framework in software, it doesn't matter if it would be safe, practical or even make sense in the real world... as long as you like it.
For example, putting EL34s in a Recto is an easy, real world option, but messing with it beyond that is much less so. Don't stop at the edges of the commonly possible unless you want to imitate something I say. Sometimes I do want that, sometimes I push beyond that.
The Fractal amps have always been some of my go to sounds b/c they are idealized. We have enough copies of copies, and great ones at that. Lets also do new things.