Part one of my audio/video upgrade...

[1oldman]

Installed: Pioneer
AVH- P8400BT
Pioneer ND-BC5 backup camera
Precision Power 4 channel amp (being replaced by a 5 CH amp)
Axxess steering wheel controller
Serius/XM tuner

Next:
CDT 6.5" components
CDT 6.5" subs (in rear doors)

A month later:

Massive Audio 5 Channel Amp
Custom 10" Stealth Sub Box
JL Audio 6W10V2 4ohm sub

Just changing the head unit made a huge difference in the quality of the sound, the amp didn't hurt either. Bluetooth works flawlessly. Steering wheel controls work well. The SQ of the front speakers is pretty acceptable for OEM. Will order the speakers next.

[EJ257]

Skip putting speakers in the rear doors; it messes with staging. Use that money towards deadening, instead. This write-up is for older cars, but should be similar for yours:
STI sound deadening, new tutorial - NASIOC

[1oldman]

The rear door speakers are pretty much just for sub bass and lower midrange. They help the staging by filling in the midbass the front mids can't reproduce. I never use tweeters in the rear of the car in any of my systems. I will place a center upstage speaker for voice location in the future. Thanks for the advise. I did forget to list the sound deadening I plan on using in the doors.

[mangostick]

Do the doors for sure, and the passenger floor area. The factory sound deadening ends at the middle of the front seats. Also, inside the hatch and hatch floor area (if its a hatch) Inside the C pillars is also a resonant point (again if hatch) and the roof (should only need a couple strips really dont want to add weight there). Looks like you've got the rest covered.. keep us posted and snap some pics!

[EJ257]

The rear door speakers are pretty much just for sub bass and lower midrange. They help the staging by filling in the midbass the front mids can't reproduce. I never use tweeters in the rear of my car systems. I have a degree in psychoacustics and know very well how to set a front center stage. I will place a center upstage speaker for voice location in the future. Thanks for the advise. I did forget to list the sound deadening I plan on using in the doors.

How will rear coax speakers do anything that a set of components in the front can't? Maybe I'm not following...

[MainFrame]

I think he was talking about putting 6.5" woofers in the rear doors. This shouldn't cause as much of a staging problem as coax.

[1oldman]

Correct, I'm putting in 6.5" mid bass/subs to fill the low mid to bass frequencies only. This will actually enhance the front staging. A true sub 25Hz- 70Hz will go in the trunk in a stealth box with a JL Adio 10W6v2 in a couple of months. At that time I'll rewire the rear speakers in series with the sub for some truly outstanding bass and staging.
I may also use upstage mid tweeters to further enhance the staging at some point in the future.

[KenBeanNet]

Did you use any extra unit to make the wheel controls to work? Did it work out of box? I bought a Kenwood DNX9990HD and a 2013 STI and I am unsure if I will need it when it comes in.

[1oldman]

You will need an Axxess steering wheel control to get the steering wheel controls to work with your head unit.

[KenBeanNet]

Will this work ?

Amazon.com: Metra Axxess ASWC Universal Steering Wheel Control Interface (Black): Car Electronics

[1oldman]

Yup that's the one!

[KenBeanNet]

I tried contacting Subaru for the 2013 information, does anyone know if the wireharness changed this year? And if not, does anyone have a good suggestion to a good cheap one?

[1oldman]

As far as is known there will be no changes to the STI OR WRX Until 2014.