Blue2k has posted some news about his Shell for the PSP:
The current Live Fire! version now features unlimited sized mp3's, and it will play mp3's from the default mp3 directory. As a bonus I've added a function that will make the mp3 player jump to the next song when the current song has finished playing.
Feel free to test it, it still needs some tweaking, as there might be some very tiny 'jumps' in the music. But those will be solved within the next few days. You can download it here: http://artillery-shell.com using the Live Fire! option in the menu on the left.