I do not think I can answer this but will give you my best guess:
I have seen where acid can be figured to how much base would neutralize it, these figures can be found with a simple search on the web. Most seem mole ratios.
Problem here is that we have a combination of acids and also metals in solution (which form these metal salts in solutions, also the acids change to different products losing gasses from the original acids, acids may not be consumed in the reaction, also some water is formed by the reactions, and every solution would be different, making calculating this for me almost impossible,
What I would try would be remove a certain amount of acid and titrate in the base to get PH desired now you will have how much base to neutralize the small amount of acid and be able to use ratio's to see how much base your main solution would need, adding in small portions till pH achieved (give time for reactions to complete or you may overshoot)
in refining with aqua regia I do not use ph measurement in my processing, the only time I can think of it would be needed is when someone uses urea to remove un-reacted nitric acid, which I do not use, preferring evaporation method.
For other types of processes I just measure with Ph meter.
