I usually take this approach, but it depends from case to case. First, sync up the sources and fix drift, and watch out for phase problems and delay b/w the SBD and AUD sources. Then, get to know each source's strengths and weaknesses by soloing each individually. Next, get a rough mix between the two, doesn't have to be final, but close. Then, if either source has a know issue (like boomy overbearing bass or tiring highs), start fiddling with EQ on just that source while listening to it both soloed and mixed, but pay particular attention to how it is affecting the MIXed version. Same goes for the other source. I try only to fix the most offending problems of each source by EQ'ing that source directly, but while paying particular attention to how you are affecting the mixed-down version. Then, while doing as little as absolutely needed that way, I may or may not EQ the mix on the master bus itself. But be very careful, if you don't have good monitoring, you are likely to f it up more than help. But always, always, always keep an eye on how the mix-down sounds. For example, if the SBD is lacking in bass and the AUD has too much bass, the mixdown might be perfect without any EQ at all. If you didn't pay attention to the mix as you EQ'd each source directly, you might have ended up cutting bass on the AUD and boosting bass on the SBD for no reason at all. However, you could still try that to see what sounds better. There is no right or wrong here, but my main point is to always think about how you are affecting the final mix.