Hi
As you say, refining gold is not difficult. And solving problems need good theoretical background - and it is my opinion that every refiner should know that basic chemistry, which is going on, and understand what is happening. At least some principles of redox reactions, electrochemical potentials of metals concerned + basics about basic compounds you deal with or that which can emerge in your solution while you are working.
Hoke is very good start. And generally saying, for processing gold and silver scrap originating at jeweller´s shop, it is completely sufficient information.
There are two worlds of refining - one that is held on basic and standard principles, shared openly (principal setups), maybe also some procedures included. This is here on the forum, easily accessible in literature, there are some great books issuing this subject.
Second world is world of private businesses - which rely on their confidential procedures and internal research to defend their position in the market. Yeah, they have pimped up procedures, step to step manuals for this and that, top end chemist developing new techniques etc... And yeah, they won´t share most of their findings with you. This is espetially true with refining of platinum group metals (PGMs) - as this field is order of magnitude larger and more difficult in terms of refining issues and possibilities. Again, in the first world we have general information, but these are very scarce. Usually there aren´t practically any given procedures about refining mixed feeds of PGMs. Contrary to gold and silver - abundant information, also here on the forum plethora threads with photographs of setups, ammounts of chemicals, yields, purities, solved problems, even some of our members posted series of great videos on YT (sreetips aka kadriver for example).