No, call SHERWOOD before you let CRUTCHFIELD near it. You're just missing something you aren't used to. Have you used a simple Dolby 5.1 channel reciever before?
First of all, get all the surround settings TURNED OFF so that you are just in plain old 2.0 STEREO...then work from there.
Also make sure the headphones are not on by chance (you have a Dolby double-D with a headphone over them)
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SKIP the SONOS thing until you are sure you are in simple stereo mode, then go through the manual from then on.
I think the biggest thing you are freaking out on is possibly the wrong thing to freak out on. You said you have very little volume, so make sure the speakers (are tere SPEAKERS? There is an A-965 AMP, this is a P- for PROCESSOR.
Anyway, you've got it in headphonemode or a monitor swtiched in (remember having a tape loop (or muting switch) on and nothing on the inputit then wondering why the tuner was really weak)? So perhaps it is CROSSTALK you are hearing and something isn't switched right. If you looked at the manual's front diagrams you saw that there is a way to use it like a loop, only it's not directly.
Meanwhile strip it down and start with the basics one at a time and master the unit with a tuner or CD player until you start to figure that out. I still think you have a button pushed that needs to be off for now. Call Sherwood.