I would run the preamp at 90 to 100% then increase level on the recorder until you are at about -10 or so then normalize in post.
So I'm back from the show and I just wanted to thank you all for your priceless advices.
I couldn't set the volume during the first act as it was an acoustic/solo performance.
I started running the preamp at 100%, the Edirol at unity gain (38) and checked the levels during the first song.
My right mic hit the peak several times so I just reduced the preamp gain using the knob until -6dB.
As a result, I got a great tape with no distortion