I think we should test that the speakers are making proper contact first. I dont know if you have your psp broken down this far yet but, get the face off. Get access to the speakers. There are 2 clips holding each one in (be care full these will break easy.) Use another flat probe to pry a side up with out a clip on it while putting slight pressure on the clips.
When the speaker is out get your psp back assembled as best as you can w/o the faceplate installed. Now lay the speakers onto the contact points. (before you get this far inspect your spring contacts on the speakers that they are not bent, broken or pressed in to far)
Turn psp on. put something with sound , music , w/e . Then try to get the speakers to make contact with the outputs. you might get sound you might not. sure fire test is solder wires to the contact points to a speaker or the psp speakers. You can solder to the points on the flat cable just be quick about it to not heat up the plastic around it.
Let me know how it go'es.