ok so I'm back from the Explosions in the sky show.
They were really amazing !
About the recording:
I'm now sure that a preamp or line transformers are needed with those Oktavas !
Run a pseudo ortf (110°,19cms) with one mic pointing to the left stack and the other one to the stage. The mics were 2 meters high and placed 1 meter from the stage and the stack. The band played "loud".
I was getting low levels despite the position of the mics and the fact that I used the mic in of my MD (recording at 27 out of 30).
A strong background noise is all over the recording...
Anyway, this was my very first open recording using a mic stand and my oktavas. I now have a Zefiro Inbox.
I'm just really excited about making another recording next week !
Thanks to all for your help.