I just setup a Harma Kardon HKTS 16BQ speaker system with an Onkyo TX-SR373 receiver with an older TV, and the sound coming from the back (surround) speakers is extremely faint, can’t even tell they’re working. We tried watching Harry Potter playing on TV, which we assumed would have 5.1 sound. I can’t seem to find a way to adjust the levels on the speakers (the menu on the receiver is really difficult to use), but I’m wondering whether the problem is the cable we’re using to connect th TV to the receiver. We’re using the stereo audio cable (which I think is RCA) that has red and white plugs on both ends. Do we need to be using an optical digital cable instead? Or do we need to adjust the levels manually? The auto setup with the provided mic doesn’t fix this, which makes me wonder if the cable is the problem, since some folks mentioned analog vs digital sound, but I wonder whether the back speakers would be working at all if that were the problem, and they are, though faintly. Any help is appreciated!