I’m not 100% sure, but I don’t think any of the sliders in Breakaway Personal (the technical name for the consumer version of Breakaway, aka… the software we’re talking about) are adjusting the threshold of the AGC.
It’s not really something that needs to be done because it only would effect the target gain going into the multiband section. A much more linear and effective way of doing this is to increase or decrease the "range" of the multiband section… which is adjustable in Breakaway Personal’s gui. And it should be adjusting the AGC’s range, and possibly other things as well to help compensate. Leif has much more insight on this, no doubt.
A side note: when the professional version of Breakaway comes out, you will be able to fully adjust everything. There are a few things about the pro core that are improved, such as linear-phase filtering, a complete (and awesome, industry-leading) FM output section, and a fully featured speaker controller. But for the most part, the core is the same as Breakaway Personal. Such a crazy deal for ~$30.