[BrickPig]

The 2011 and 2012 factory xB stereos have RCA-style sub woofer outputs on the back of the radio, see this thread:
http://www.newscionxb.com/129-classifieds/9692-scion-factory-2011-2012-radios.html
I use them on my 2011 for my homebrew 8" subwoofer.

 

[BrickPig]

BTW FYI when I added my sub I did not have to pull the head unit to access the RCA jacks at the rear of the head unit. Instead I removed my glove compartment door and was able to access the RCA jacks that way.

 

[BrickPig]

Where did you hook up the R.E.M wire?

If you mean where does my monoblock amp get the turn-on signal, my understanding is that the OEM head unit does not have such an output. So instead I tapped into my accessory outlet (aka cigarette lighter) as the turn-on signal. See my website below for more details. Yes that means my amp is on whenever my Acc is on, but that was the fastest and easiest way to get the turn-on signal.

BTW if someone knows a better way to get a turn-on signal from the 2011 base OEM head unit (Pioneer), please share...