Sorry I haven't been able to respond to your messages sooner -- I've been deluged with inquires about Subaru wiring and my harnesses. I'm trying to get more information on my site to reduce the amount of questions.
Side of OEM nav from a 2010 Legact GT (posted by "BigBopper"):
(the upper box is the OEM satellite radio tuner, attached with the brackets included in the kit).
Rear of main body that another 2010 Legacy owner sent me:
(I actually supplied harnesses he used to "transplant" that in place of his OEM non-nav head unit).
The rear connectors are somewhat similar to those on Subaru's earlier OEM Kenwood nav HUs (including those in 2008-up Imprezas and Foresters), except this Legacy/Outback nav uses Subaru's newer-style 20-pin power/speaker harness (vs. the older 14-pin).
I can build harnesses you can use to retain your factory 3.5mm aux jack and OEM rear camera (in addition to supplying the 20-pin power/speaker harness with SWC wires).
It had been thought that you needed to send line-level (unamplified) signals to the factory harman/kardon amplifier. Thus the reason Crutchfield was recommending you use the Metra 70-7553 harness (with RCA plugs instead of plain speaker wires). However, people have found that the OEM HUs in cars with the h/k system actually send high-level (amplified) signals to the h/k amp.
People have connected aftermarket HUs both ways, and the h/k amp works. I haven't heard from anyone who tried an A/B test to compare.
The OEM nav's mic is built into the unit. Even if the factory mic were in the map light cluster (as it is in some models/years), you would want to use your new HU's mic instead. It's really not that hard to "tuck" the mic's wire behind the trim to run it up to near your mirror. I recommend testing different locations first -- you might find a different spot sounds better to your callers.
Unfortunately, the car's USB connects to a strange small black socket -- at the lower right in the above picture. It may be the same style connector Kenwood uses on some of their other aftermarket HUs. However, that doesn't really help -- the only cable they would offer is one to plug into the back of the HU. You would want the opposite gender to connect to your car's factory USB harness.
The easier option would be to change to an alternate center console aux+USB "pod" that has a standard USB "A" socket on the bottom. See this thread
, and the one I link to at the end.
switch to a different OEM USB harness used in 2012-up models. It has a plug at the HU end that Imprezas and Foresters have used, and for which I have adapters available. But the OEM cable is very
Another possibility is to transplant the 2012 or 2013 non-nav OEM HU with 4.3" screen. I've sorted out the harnesses needed to do that swap -- see this thread
Regardless of whether you switch to a different OEM HU or an aftermarket HU, you will indeed need to switch to the OEM non-nav style fascia. If you will be going to an aftermarket HU, you'll need an aftermarket double-DIN dash kit in addition to that.
You can sell both your OEM nav and fascia together (along with your GPS antenna, which is not difficult to remove). Legacy/Outback owners who want to transplant the OEM nav would be interested in that whole set.