Someone may have a better idea, but it either sounds like the output voltage on the AVR isn't right, or the auto sense on the amp is not working correctly. I'd lean toward the amp since you get boom with it set to On. That tells me output voltage on the AVR should be OK, because if it wasn't you would not get much or any output from the sub regardless of Auto or On.
Maybe Hsu can help you reign it in. If your trim level in the AVR is set to 0.0, the sub should turn on just fine with volume.
65" VT50 / BDT460
X4000 / Outlaw Model 7125
Klipsch RF82 II and RC62 II / Hsu VTF-15H (2)
Directv HR44-200 / HR24-500