Just bought this system used, don't understand the Bass-Treble-Loudness??? controls on the Left Main speaker - there are green lights in columns below the grill that go on and off when I operate these control buttons but no real indication of which direction I'm going. There's a knob to the right that has + and - but again, no way of knowing if this is controlling bass or treble, etc. I'm sure it's simple, but not obvious at this point. Thanks in advance, ebuckler@icehouse.net Ernie B.