I believe the 500 does have a "remote" jack just like my 600. This usually consists of a 12V trigger and comes from your receiver. When you turn the receiver on, a 12V pulse wakes up the sub. I haven't tried this so I don't know how good it works.
I would guess that the power consumption at idle is about 10W. I'm not even sure if the power consumption goes to zero with the switch turned off. Many devices nowadays have the switch on the secondary of the power transformer to keep the size of the switch smaller. So the primary is always connected and draws a small amount of power.
