I ended up getting it real close, but since the onstage mics picked the ambient sound of the snare hits plus the PA, it's a compromise at best.
keep in mind that the time signatures (unless the mics were in the same stands in the exact same place) on stereo pairs on stage will always be different and so its sort of impossible to be perfect matching them up. That made me crazy enough that I started picking the best sounding pair and ditching the other.....eventually I stopped recording more than 1 set on stage for that reason.
ETA: I think we ^^ just said the same thing....
Yeah, the less isolation between pairs, the more the relative differences of timing within each pair play against each other once they are combined. As more sources with common information are mixed together, the more complex the relative timing interactions become. Unless the microphone arrangements or combinations are planned specifically with that in mind, things may work out well or may become problematic as more pairs are brought into the mix and the various timing combinations interact. The only thing one can do is try various sync relationships to find what works best for that particular situation- it might be syncing one set of relative arrivals instead of another set for the same instrument or sound-source, or simply leaving out some recorded channels as Jim notes.
One thing to think about in that light is how many sources with essentially the same information in them you really need before the complications become over difficult to manage? If you have both an on-stage pair and a direct SBD feed, you have essentially all elements of the direct sound from the band well covered. At that point the AUD pair becomes mostly useful for providing ambient room and audience reaction sound. Direct pickup of the PA in the AUD is then redundant information and may simply aggravate things more than benefiting them. When that's the case, using a setup like spaced omnis for the AUD pair, or pointing directional mics out into the room from onstage, away from the band and PA, or even turning a typical cardioid near-spaced AUD pair around to face away from the band and PA might be more useful than a typical AUD setup of near-spaced cardioids facing the stage.
But It's always nice to have a normal AUD pair as a redundant fall-back safety if other things go wrong, and the value of that can't be overlooked.
I align things more or less like a-jack notes above. Snare hits and speech are what I'm looking for. Speech is usually the easiest source for me to hear immediately and get the timing just right, as long as it is heard well enough in all channels.