Since no one has responded, I'll admit that I have no idea what this does but I'd love to know. Based on the name, I'd guess that it removes DC offset? But that's just a guess. I thought maybe it was some kind of sophisticated dc offset mains filter, but the reference to "+12V" (input/output?) in the schematic makes me question that.
It goes to prove my theory, that no body will want to do DIY anything soon, because it appears our skills have diminished, sad world,
Right the odd circuit detects the audio on your DIY amp and turns the power on but there are other controls on the PCB to allow use with out tearing apart you FAB new non DIY amp from China he he, That turn on and turn or time out. Have fun.