The amp is connected via a 21pin DIN that i have the pinouts for but can't find a female connector to make the break-out cabe for.
The loom going into the back of the McIntosh is standard Subaru though, so if you have a Subaru to ISO you can at least plug in std power, acc, dim, etc but the speakers won't work.
Upgrading the MY07 GTB stereo gets costly after you do the basics (speakers and deadening).