I think that the usual old Mathcad Users Guide and Reference Manual suffice for advanced solving. Yes, there are a few more options available - maybe do a keyword search in online help too. The examples are pretty illustrative too.
There are a few places you can look for more information on these functions. If you search for maximize function in Help, there are a couple of pages that should give you what you want. There are some QuickSheets under the Solving section in the Resource Center, and under Tutorials in the Resource Center, check the Solving chapter from the Mathcad Treasury. The section on optimization explains how to use features of the Solving and Optimizing Extension Pack.
I suppose the most powerful optimization method in Mathcad is the conjugate gradient method. I believe, this is the Fletcher-Powell algorithm. I have the original article by Fletcher and Powell and the method is also contained in the "Numerical Recipes" book.