Homebrew dev plum released a new version of the Mp3PlayerPlugin v1.5 for 5.00 M33, 5.03HEN, 5.50GEN, 6.20TN and 6.35 PRO!
With this plugin you're able to hear your own music in PSP games.
Controls (translated by me):own when you change the volume by pressing the key length can be changed in any emulator software, too HOMEBREW Fixed a bug that freezes was to work
DownloadL + R + Left / Right = select other songs
2. L + R +  = Pause
3. L + R + O = Change the order of play (in order, randomly, etc.)
4. L + R + Triangle = Play the song again.
5. L + R + Up / Down = change in volume.