As the title states, is it possible to wire an aftermarket sub/amp combo into the stock head unit?

I figured it wouldn't be impossible because Subaru does offer a sub/amp combo, so I figured the wires may already be run (except the battery power obviously).

Any links to any other informative sites/tutorials would be really great.

Thanks in advance!

The wires are not already run, they come with the Subaru amp. Yes, you can do it: the basic idea is to get *high-quality* LOC's or LLC's (Line-Output Converters or Line-Level Converters) which step the wide speaker-level voltage range coming out of the HU to the smaller range used in standard amps. Do a search on this forum for "LOC" and/or "aftermarket sub".

Excellent! Thanks for the info!

Anyone else?