You could check into Rockbox as an Application
. You can get apk files at various resolutions here. http://forums.rockbox.org/index.php?topic=28315.0
There's no theme site like for the other builds. I believe there's some in that thread and some here.
TBH it's somewhat buggy. If I hadn't experienced Rockbox before I probably wouldn't have gone through the hassle to get it up and going on my Android devices. The UI isn't the most intuitive or the prettiest but the parametric EQ isn't matched by any other I've experienced on an Android or any other portable device.