Thanks for the insight.
The subs are not separated. They're on the main floor, centered directly in front of the stage, one stacked on top of the other. I can add delay with the VSX26 to get both subs in phase, to correct for the Crown's DSP latency. That'll require two different sends to the subs instead of one, but that's what we were doing all along before getting rid of the the little PRX powered sub.
So far, however, I haven't powered the subs with two different amps. Just to see what it sounded like, I used the Crest Pro8200 in stereo mode to run both subs last Sunday. I know that two STX828S subs are really underpowered using that amp for both, but I was curious to hear what it was capable of, since several people have suggested ditching the Crown.
Underpowered as that setup may be, it was more than adequate for our needs. (The music runs a little loud at my church, but we're not loud like an all-out rock concert!) I ran a few different low freq. test signals through the subs and was surprised at how noticeable the difference was between the Crown XTi4002 (from previous tests) and the Crest Pro8200. Specifically, when I muted the signal, the sound stopped noticeably faster, as if the room were a little less reverberant. That's what I was hoping for, to tighten up the bass. Next week I plan to use both amps and A/B the subs to see if the tighter bass response is as pronounced as it I think it is.
