It is true that optical is mostly settings-free, setup wise. From your description you have at least verified that the optical input on your receiver is working when you were using your cable box. Are you using the same optical cable as you had previously connected from the cable box? Have you tried another optical cable? With the optical cable plugged into the TV, do you see light coming from the other unconnected end of the cable? In your TV menu Settings, Audio, what do you see with Auto Detect? And of course, are you switching the receiver input to the input source for the optical input?