Use stock sub with aftermarket head unit

I just purchased a new Sony XAV‑AX100 head unit into my 4runner. Problem i am running into is the stock sub does not work. I was told by installers (best buy unfortunatly) that the stock wiring for the sub goes into wiring harness, and does not get controlled through the sub output. How have other people gone about using stock sub with aftermarket harness?


I have 2007 4runner sport with JBL 10 speaker audio system.

 

Been researching after market head units cause I really don't like entune. I believe you need the idata link meastro to retain the factory sub.

 

This looks like a wiring harness? i know just enough to be dangerous . is this a module for the sub specific? all other speakers work just fine.

 

It hooks up to the harness. The modual keeps steering wheel controls and a bunch of other stuff. This is the site that tells you what it will interface with:
http://maestro.idatalink.com/search...07&vehicle_model_id=146&vehicle_audio_id=4204

For the record I haven't installed this yet. It's on my mod list though so I'll get there at some point