Could the person running the mixer record it at the same time?
Herein lies the problem of not having all of the instruments fed through the mixer. While this is a jam event, not formal by any means, I struggled with this problem when we were broadcasting the jam on the grounds. I took me about 2 years (4 jams) of practice to get the right balance of sound on the wire. But we were successful and had a great quality stereo mix being sent over for broadcast. Of course the broadcast mix was different then the house mix, but I think it often sounded better and balanced out the differences in levels. Then, as now there were a few instruments fed directly into the mixer, but the rest were picked up by as many as 9 microphones planted around the room and allowed the ability to turn down someone that was a little loud and bring up someone that was a little low, relatively speaking, like an acoustic instrument or a keyboard. This problem is why you see posts time and time again begging players to bring only small amps and to not play with overwhelming volume. It's pretty easy to max out the small room.
Of course it would help if there were the opportunity to get together for a practice session or two beforehand to get an idea who is coming, what they are bringing and what to practice, however this is the real world and it would be quite a chore to get people together from all around the northeast for a few hours or a day to "pre-jam" before the main event. Everybody's busy nowadays.
It's been a bit over 2 years since the last broadcast of the jam and while I could install all of the necessary equipment to get a good mix in the can or nowadays "in the stick", it's a lot of extra work and a good deal more equipment to deploy.
What say you all?
-Ben
da mixer guy
