Trouble-shooting 1522 amp
If all the connections are good and the same as before it quick working....the best guess would be a failure in the DC Tracking Amp Power Supply that supplies power to all the individual amplifier channels. This would take down all channels except LFE (which isn't amplified).
The reason I suggested trying the headphones is that you also wouldn't be using the main amplifier.
So why don't you divide the problem in half like most good trouble-shooting procedures. Is it in the pre-amp section or the amplifier section?
Use a self -powered speaker (like from a computer speaker system or similar). Plug this powered speaker into the RCA jack of the Right, Left orCenter-Out section of the Pre-Amp out section on the back of your amplifier. (If your speaker uses a 1/8"mini-plug input, then get a 1/8" mini-jack to RCA plug adaptor.) Making sure this speaker is on, play some, preferrably 5.1, sound. If you hear output through the speaker then you have a main amplifier problem like I was describing above.
If you don't have sound then you have a Pre-Amp problem....simple as that.