Hi Chris,
It sounds like you have a satnav unit similar to the one shown in
this thread.
Is the "aux plug" you added Subaru's OEM "Cord Convert" harness (see post #3 in that thread)? And is that aux input what you're using for your iPod, or did you also add something else to connect the iPod to the HU?
In
that NASIOC thread you linked to, the green subwoofer RCA jack shown in my post is equivalent to the red "SUB WOOFER" jack on the OEM cord convert harness.
Had you not installed the cord convert harness, you could have added my RCA cable to your Liberty's 24-pin satnav harness. But since you have the cord convert harness, you don't need my RCA cable (in fact, my cable would not work, since the cord convert harness would prevent mine from connecting to your HU).
The rectangular-shaped OEM sub will not work with the satnav's line-level subwoofer output. See
my post here (#4 in my 'Subaru stock HU info' thread). You can install that sub and it will function, but it taps your satnav's front speaker outputs. Your on-screen menus
will not control that type of sub!
So why is the subwoofer output present on these OEM Kenwood satnavs? I suspect it's only used in some JDM model Legacys and Outbacks. On the similar Impreza/Forester Navi, I've only seen it used on some Foresters. Perhaps some JDM Imprezas use it too (it seems JDM Subarus get many more options than the rest of the world).
If you really want to be able to use your satnav's subwoofer output (so you can control a subwoofer via the on-screen menus), you must choose a different sub -- either an aftermarket sub (one that can accept a line-level signal as input), or the OEM "odd-shaped" sub
shown here.
With the latter, you would need to build a custom harness. It would convert from the subwoofer connectors* on the "cord convert" cable to the proprietary 6-pin connector on that "odd-shaped" OEM sub.
*Specifically, the red subwoofer RCA jack and the sub "power control terminal" (remote turn-on lead -- the blue wire with female bullet connector). You would also need to supply that sub with +12V tapped from somewhere in your Liberty (and chassis ground).
For an aftermarket subwoofer, check out the Sound Ordnance B-8PT. That has received many favorable reviews.
If/when you pull your HU again, I'd greatly appreciate pictures of the entire front, back, and top (with label with model numbers).