From what I understood was that the amount of Acidic acid produced by Brett is minimal even in the presence of O2, most souring comes from Lacto and pediococcus. High levels of acidic acid indicates that acetobacter is present. Also the pellicle layer formed by Brett acts as an O2 barrier as well as protecting the beer from Acetobacter.
From what I have read, Pediococcus will do the majority of the souring for lambic's by producing Lactic but can produce a lot of diacetyl at the same time too. O2 inhibits pedio's growth, so a good balance of O2 in the system will get you a good sour with minimal diacetyl. though with time the brett will clean up the diacetyl, but that can take a long time, at least from my experience.
RJSky, I agree that under the home brewing conditions we need to consider the size of our batches and the limitations of our equipment, but we also need to strive to create a similar environment to how these beers where made. Lambics and other sour beers are a product of a complex interaction between several different micro organisms all influencing eachother over the life of the beer.
Steve Piatz gave a good talk at NHC 2010
that gives a good schematic of these interactions.