Here is a brief write up from my Crutchfield buddy for our Shaker 500/1000 systems.
2005-Up Mustang Shaker Systems
As far as factory premium audio systems go, the Shaker 500 and Shaker 1000 systems offered by Ford in the 2005-Up Mustangs are some of the better ones out there. They provide a great amount of midrange and lows, but as with most factory equipment, the highs are lacking.
That being said, the first and best improvement is to replace the front and rear 6x8 speakers with aftermarket models. These speakers are powered by the factory stereo directly and receive between 15-20 watts each. Since we’re just looking for better clarity, it’s really not necessary to purchase hi-power (aka “expensive”) speakers to achieve the improvement that I’m talking about, but for those that want even more, that option does exist.
Instead of just replacing the 6x8 speakers, high-quality 5-1/4” components can be used along with a separate four-channel amp to bring the upper-midrange and highs up to the level of the lows. The 5-1/4” speakers will require adaptor brackets and the tweeter will require custom mounting, but the increase in sound definition would be noticeable.
Another way to increase the overall quality is to line the metal surfaces, for example your trunk walls and door steel, with a product such as Dynamat. A car’s body panels have a tendency to resonate when your music is playing and a significant amount of the sound energy is lost. On top of that, you get the benefit of keeping annoying road noise out of your car. When these panels are deadened, it will seem as if you’ve added more power to your system.
And last, but not least, is the replacement of the factory head unit. Most people feel that the factory head units in most cars leave something to be desired. Some want advanced navigation, others an easy iPod or satellite radio interface, or just a better looking and sounding stereo. The options for the Mustang are plentiful and include single or double DIN-sized stereos that allow you to retain the use of the rest of your Shaker audio system.