We already talked about Sony's xLoud Audio Engine for making your HTC EVO sound louder, so now let's talk about making it sound better?
If you've ever been jealous of HTC Rezound users for their built-in Beats Audio experience, you don't have to be anymore. Some custom EVO 3D and 4G ROMs already have Beats included, but not every ROM could support it (especially AOSP ones) . . . before now. Android developer RockoDev has managed to find the right binary and library files to make Beats Audio compatible with all Gingerbread ROMs. The only requirement for HTC EVOs is that you are rooted.
You are going to see the most sound improvement in high-end headphones, and some people are generally skeptical of whether Beats Audio is little more than a marketing campaign, but I personally think it makes my EVO sound better.
Update: I have found the original thread where this was from. RockoDev just put out a new version today that also includes Xloud. Check it out above!