New 2012 GT and a stereo question

Lots of people upgrade the 5x7's with a large degree of success. It cleans up some of the "muddiness" of the stock speakers. Popular replacements seems to be Pioneer TS-D6802R, Polk Polk DB571 and Infinity Kappas but really an 5x7 should do. I have not done this myself as the sound from the stock speakers is quite enough for me.

Yeah, replacing the head unit isn't possible on it's own. You need a replacement control panel for the AC, etc. There is only one option that I know of although Scosche is supposed to have another soon. Either way you lose all Sync functionality if you replace the head unit as well. In my opinion you are better off just replacing speakers/adding amps if it is enough for you.

What I did was got the pioneer single din headunit DEH-6300 UB and then also bought a kit to make it fit the double din hole in the mustang so now there is an area where i put my headunits remote and my phone/ipod when its plugged into the radio. I also got the alpine mrp 500 amp and 2 rockford fosgate 12 inch subs. They hit very hard and im planning on getting new speakers soon, i havent decided which ones yet but they will most likely be pioneer, alpine, or memphis. hope this helps!

That's a much easier proposition on the 2005-2009 than in the 2010+. The integration of the AC controls on the same panel as the stereo controls complicates things massively. You can't just replace the head unit.

stereo

Ckeck out the Kicker stereo for new Mustangs and Shelbys.

Use the existing head unit but add a 200w amplifier (under the dash). change out all the speakers to new Kicker units, Add Kicker 200w powered sub-woofer to the right side of the trunk.

I put this system in my 08 GT and now my new 2011 GT. Did not drill a single hole, get out a hammer, or cut up anything.

Sound is excellent, quality is great, entirely invisible once in the car, price is right, and golf clubs still fit in trunk!

csm

I wanted to keep the head unit intact for looks and features, but it has no preamp outputs, so I had a JL Audio XD 700/5 amplifier installed under the passenger seat. It can take either line level or speaker level inputs. The installers tapped into the speaker lines on the way to the door and diverted to the amplifier, then back to the door speakers. I also replaced the door speakers with component speakers, with the tweeters floating on a bracket over the woofers. I replaced the rear speakers (in my case the rear quarterpanel speakers since I have convertible) with 6x8 2-ways.

The amplifier can handle 5 channels (with 6 outputs), so the new amp now powers all four speakers and the two door subwoofers. I'll eventually replace the door subwoofers also with Kenwood Excelons in the same location, but the factory subwoofers sound better with more power.

So, the end result is no disturbance of the dashboard, no visible sign that anything is other than stock (unless you look under the passenger seat), and a very much improved sound.

I am very happy with this setup, but the only warning I would have if you do something like this is to use a very reputable installer. This is not a Best Buy type of job. It's pretty tight working space to get at and tap those wires and you want someone who will take the time to do a good soldering job in that tight spaces and leave a neatly finished product. I went with a local high end installer.