This walkthrough is designed for someone who would like to replace their OEM HU with a 2-din Aftermarket HU and not tap/cut/splice any factory wires. We will also go over retention of factory USB, AUX, and steering wheel controls.Finding the right HU for you is essential. In my research, I have come across more people going with Pioneer than any other brand. Doesn't surprise me considering they make some amazing hardware. I personally went with the Pioneer AVH-X5500BHS mainly because it was on sale at the time and has everything I was looking for.When replacing the head unit of an 08+ WRX from the stock HU you have two options as far as fittings go.Usually when you purchase a head unit online you are given the option to also purchase the dash-fitting kit. Unfortunately, on the wrx, the stock HU bezel (the piece that surrounds the HU) leaves a pretty unsightly gap that these dash kits have to fill.Here is an example of this gapNow this may not bother some people but if you are like me, you want it to look as clean as possible. The other option you have is to replace the Bezel itself with one made specifically for a 2-DIN stereo. You can purchase this 2-DIN bezels from a select few online dealers but unfortunately none are located in the US. I purchased mine from AVOjdm for around $70 and received it within a week.Here is a picture showing the difference.Picture of what the replacement bezel looks like installed.A lot has been discussed on retaining factory hardware. If you are like me and would rather not mess with any factory wires whatsoever, you pretty much have one option. Hit up SVXdc for the adapters. He is the only name in the game as far as one stop shopping goes for all your Subaru audio needs. Once you know exactly what you need, just shoot him an email with an item list.To retain USB is kind-of a pain in the ass. It will require you to solder your own wires but it's actually a pretty easy process so don't be scared to tackle it yourself.Items you will need:-Soldering Iron/solder- Hirose Connector (purchase from SVXdc)- hot glue/ glue gun- electrical tape- old USB cableAll you have to do is solder the following (the Hirose connector is labeled 1-4 and the outside is ground.Connect the end of an old USB cable you cut to the following pins:1. Black2. Red3. Green4. WhiteThanks to MtnXfreeride and his walkthrough and Dan5505's 2013 WRX Build Thread , here are a few pics showing the process.Take an old USB cable, pretty much any USB cable will work, and cut it about 6-12 inches down. This is what should be inside.Solder the wires onto the corresponding number listed aboveHot glue works best but use something to keep the wires secure and thermal.End product.Now all that's left is to connect the adapter to the end of the stock USB cable and the USB end into the back of your new HU.This is the easy one. All you need to do is purchase the pre-made adapter from SVXdc. This adapter can be used with any HU with an RCA AUX connector on the back.To retain your steering control you will need to purchase an adapter that converts the signal from your controls so your new HU can read them.The only solution for this is to Purchase an ASWC-1 kit When you begin to hook up your wiring harness, you will just be adding a few of the wires from the ASXC-1 into the mix.Here are the direction straight from SVXdc on what wires to attach where. (Do not use the direction that come with the ASWC-1)Things you will need:- Soldering utensils or butt connector- Crimper/wire stripper- Electrical tape- Shrink tubingIf you are purchasing from Crutchfield, they usually throw in the wiring harness and dash kit for free. Thats cool and all but you will be missing some important wires that the ASWC requires to retain steering wheel controls. My suggestion is to purchase the HU from Amazon of something for slightly cheaper and purchase your Harness from SVXdc. His come equipped with all the wires required for connecting the ASWC.Here is a picture showing the 3 extra wires on the SVXdc harness required to use the ASWC-1You will have 2 harnesses. One that came with your HU that connects to it, and the other from SVXdc that connects to your stock wiring.You have 2 options on connecting the wires together. Solder, and Butt connectors. I like solder. I feel it is more durable and easier to work with, but there are people who would disagree. Either way all you will need to do is connect the corresponding colors together and somehow secure the connection.Keep in mind if you are installing an ASWC-1 you will be adding some additional wires. Make sure before you secure a connection with solder or a butt connector, you double check you have all the wires connected. Once again, here is SVXdc's instructions on installing the ASWC-1If you are purchasing a DVD capable HU or for some reason you have a super long bright green wire attached to your HU's wiring harness that says "emergency brake" on it, this is a safety precaution that prevents you from accessing some functions on your HU (like playing DVDs while driving and getting too deep into menus) unless the parking break is on. It usually has a vampire clip on the end of it and, once again if you are like me, you refuse to tap into any factory wires. Luckily the make little micro Parking Brake Override Bypass units that you wire directly to one of the harnesses.These are model specific so make sure you get one that corresponds to your HU's model.This thing is simple to hook up but keep in mind, you will be adding these wires into the mix of other wires when connecting your harnesses together. Don't forget to double/triple check when it has come time to hook it up. Unlike the ASWC-1 you CAN use the directions that come with it.Unfortunately, as of right now there isn't a method to retaining the factory bluetooth microphone. There are a few threads of people attempting to solve the problem however. Most HUs come with their own bluetooth mic. Many threads have been started on finding the best spot to put it.There was one person who briefly popped into a forum saying he routed it to where the factory mic is located (middle of the dome lights), moved the factory mic out of the way, and used some double sided sticky foam to adhere it in place. At some point I hope to attempt this and eventually update with a quick walkthrough.(UPDATE) Just finished a walkthrough on replacing the factory Bluetooth mic with your new mic in the factory location. Check it out here! Items to request form SVXdc ( order info page : scroll down for e-mail address)- 20-pin harness- AUX adapter- USB connectorOther items- Parking Brake Override Bypass (look up by model number of your head unit on amazon) ASWC-1 (can also purchase from SVXdc or Amazon)- Tools for soldering or butt connectorsThats it. Thats all the info you should need to replace your head unit and retain all your factory goodies (other than bluetooth)- oOTAGOo