I have actually had good luck with 4 mic mixes. Here are my thoughts on the subject.
-As far as the mics used in the mixes, I'm a bit of a purest. I like to use the same brand mics throughout. My most recent endeavors have been with my Neumann u89i's and borrowed pair of Neumann km184's (fixed cardioid). Not to say I don't like other brands, I just like don't like the idea of mixing.
-I don't like to use the same pickup patterns and I configure my mics so that it is an all or nothing fashion. Basically, I don't use traditional mic placements like DIN, DINa, ORTF, etc. Actually, I never run those patterns because those techniques or theories are based on precise numbers/angles and, in our situation, we are almost never in a 'perfect equilateral triangle' with the stacks or source. That is a whole other subject in itself. Anway, I positioned the mics so that neither source would sound good on its own, but in a mix the 2 would compliment each other.
-For WSP 04-15-07, I ran the km184's XY at like 60 or 70 degrees. They were pointed well inside the stacks. I wanted a tight sound from the km184's by picking up as much of the stacks as possible with as little of the room sound as possible. As for the u89i's, I ran them about 1.5' apart, angled wide, with subcards. My intentions were to pick up as much of the room acoustics as possible and at the same time capture School's bass. As I thought, the km184 source picks up the PA system, but leans more towards a mono recording. The u89i source sounds more like an ambient room recording. I would not be happy listening to either on there own, they're both lacking. Together however, it is one of the best, if not the best AUD recording I've made. You clearly hear the attack from the PA and the decay through the room.
-I always mix the sources in post. I don't EQ, just mix.
That is all for now. I have other things to do.