Using a sound enhancer application would do no good because these applications are made with one purpose in mind: to monetize the profit upon selling. You can try some of them using the Google Play market but after a while you will notice that the quality is the same although you apply the filter they have. The best application which actually does something to the quality of the sound is DSP Manager which is developed by the users at XDA Developers website. By default the application is found in the CyanogenMod Rom but you can try and search for a version which is good for your phone on the forums I mentioned.
