With my GL2, a DXA-8, access to house mixers, deployment of one or two AT3031s, and some experience under my belt, I've begun to get some very decent audio with my footage (Jazz and choral concerts, musicals). But I'm greedy for better.

In my two main venues I've been taking the post fade, post mute, post EQ mono out from the board into one channel and an AT3031 for room ambience at my camera position at the rear of the auditorium into the other. In post, I delay the mixer channel by 40-50 miliseconds to compensate for the speed of sound through the air in reaching the AT3031, which I find to be significant. The results have been very good. Besides livening the board's otherwise dry sound by adding room character and audience noise, the ambience mic helps smooth over any coverage deficiencies in house mic placement on the stage.

But two improvements I think I could make are:

1. to take stereo from the mixer when available, and to add the ambience mic to both channels. If I can add some stereo imaging to the basic quality I'm getting now, that would be a plus.
QUESTION: do you think a three-channel mixer feeding my cam's two channels would be the best approach, or would it be better to go with recording the ambience on a third track with my second cam for more flexibility in post?

2. to move the ambience mic up to the front on the general principle that closer to the source is better.
QUESTIONS:
a) Am I correct in thinking a good omni would be a better choice than the AT3031 in that position?
b) If so, is a good wireless omni lav good enough for music content and dynamics? Besides the setup convenience in these situations, a wireless would add other capabilities to my toolkit.