There's a theoretical manual in the install that summarizes the fundamental math behind the solution methods. It's accessible through Help>Simulation>Validation>Theoretical Manual. You'll need to have Simulation added in, and a part or assembly open in order to see the menu option.
It doesn't get into the detail of comparing the different solution methods, but should give you an idea of the fundamental physics being solved for. Warning, it gets pretty dense pretty quickly.
Thanks that is exactly what I was looking for.