Might be he wants a sound "larger then life" or just something different from the crop.If all mics are used, there are certainly some sound colorations due to phase cancelations that change when he moves around.Like a multistage Phaser FX.Gefell builds a condenser mic line array to improve directivity, used, for example, in the German parliament, the "Bundestag". This is not 100% comparable, but these 7 mics could point into the same direction.It's likely that these 7 mics improve the feedback rejection in a PA situation.And - what about the "lucky no. 7"?