It didn't really sound much better with Class A on to my ears, maybe just a >hair< warmer for the same SPL. I was never disappointed with the way it sounded. Just be sure to only turn that on/off while the unit is off.
The REQ knob I don't recall what it should be set to, but I believe it was off normally. I'd try switching it too, to see if setting it to source works. Try the inputs other than AUX as well, as any of those analogs should work.