The Exiga satnav is very similar to those used in 2008-2011 Imprezas and Foresters (and some 2012). See 2nd half of
this post for more info (in my 'Subaru stock head unit info' thread on NASIOC).
I think the Exiga uses the aux A/V input for the RSE (rear seat entertainment) system. Does yours have that?
If not, that could mean you have the OEM "Cord Convert" cable installed, which added RCA jacks for the aux input behind the HU (Google "H0010AG100", which is the OEM part number). You might want to pull your HU and take a look to see what's back there. If you do, please post pictures.
Whatever you find, I can probably make an adapter harness of some sort.
Does the Exiga have a spot for a factory 3.5mm aux jack? If one was not included on yours, there may still be a spot with a blank plate for the OEM jack (likely inside the armrest console).