Many times people post saying there must be something wrong with their hardware, when usually it can be traced to CONNECTIONS.
Here's the classic "fix" for sub AUTO-ON.
(To review, as you know, the Auto-On feature allows the sub amp to sleep after a set period of no signal. Usually a LED lite goes from red to green or viceversa. It's left in standby 24/7)
Some subs wont power up when a new signal is sent because the SWFR LEVEL setting in the receiver's remote set-up menu is set too near the bottom of the scale.
The trick is to raise this about 6dB and then recalibrate (Yes, you have to do this) the sub with a SPL meter by turning down the sub amp's knob to compensate.
As a last resort, others also will get a RadioShack Y-Splitter (Female to 2 Male)to boost the SUBOUT cable signal to the sub amp's L&R. Otherwise a splitter isnt needed.