Using sauce as a soup base
Very simply, all of them work. 

The major driver of what tastes good to you is expectations. If you are accustomed to eating soup with a certain taste, and expect it to taste that way, then any time you prepare the soup with something different, it won't taste good to you. 

But there is no rule to define that some liquids taste good as a soup base and others taste bad, universally. And without knowing how you like your soup, it is impossible to predict which ones you will like personally. 

Update In the edit you mention that it is the concentration that is wrong for you, not the flavour profile altogether. 

What gives the soup flavour is not the liquid part. In fact, the liquid in both sauces and commercially available "soup base" as well as fond, stock and other similar stuff is pure, tasteless water. The taste comes from whatever is dissolved in the water. 

Whatever you are using as a soup base seems to be just much more concentrated than the sauce. It is very probable indeed that one of the things which don't have enough concentration for your taste in the sauce is salt, another one is probably MSG. But also other flavour bearing compounds are probably provided in less concentration in the sauce. After all, the sauce is supposed to be poured over solid food, and shouldn't taste bad when you lick it off the food surface, it is at a concentration which doesn't taste too bad when it comes in contact with your tongue. The soup base is at a concentration which after dilution falls in the commonly acceptable range (but at a lower concentration than undiluted sauce).