Truth is, so far AFAIK nobody made a side-by-side test to show whether the initial acid soak presents any benefit in terms of yield, as opposed to for example just going STB.
I have the feeling that for powdered bark there will be very little or no difference at all. In that case, maybe it would make no difference to add fumaric acid or vinegar. With bark in pieces it might make a difference though (but anyways its recommended to blend/powder the bark before extracting).
More testing would be necessary. If you wanna do a side-by-side extraction yourself, do let us know the results
