Well, at a high level, I basically just want to be able to crossfade
two audio sources (we'll call them A and B) so that as A becomes
"louder," B becomes "softer." I was under the impression that could
easily be accomplished with a pot. In this case, input A (coming
directly from the output pin of an opamp) would be connected to the
1st lug of the pot, input B (coming from the output of another opamp)
would be connected to the 3rd lug, and the shared 2nd lug would be
connected directly to the input of a third opamp which would act as a
buffer and send the crossfaded signal on its way. Since you
questioned it, is there any reason why that sort of setup wouldn't
accomplish what I want? Or did I just not explain the scenario well
enough up front?

I think that is basically what the crossfader is a DJ mixer is - a
dual gang (for stereo) slider-style potentiometer. Assuming that
approach would work, what I was really asking about was whether there
are any complications I hadn't thought about. I don't think I should
need any pull down resistors or anything of the sort.

-Brandon