.:[Playing Snes Music on your PSP]:.
First thing you have to do is get yourself some good Snes Music, so head over to Zophar.net and pick up your favorite Snes video game music in zip format.
When you download the files to your computer they will be in .spc form which is standard for snes music. If you have a spc player for winamp (which you should have got while at zophars music directory
Download SPC2ROM
Put SPC2ROM in the folder that you have your Snes SPC sound files. To convert the file from the sound file data that was originally ripped from the rom, back to a standard rom file. (you must type this from the dos prompt or in a command box in windows)
Without quotes type "spc2rom -P soundfile.spc outputfile"
spc2rom is the converter
-P is a command that buffers the rom so that it is a standard size
soundfile.spc is the file you would like turned into a playable emu sound file
outputfile will be outputted as filename.SMC which is a snes rom filetype
It is mandatory that you use -P, if you don't the file WILL NOT work.
This will create a SMC file with the track held inside, now you may zip the .smc file by itself to compress it. Do no be alarmed by the filesize. A typical song could be around 44 kbytes when zipped but will play just as good as a mp3 in high quality 44k audio, once on the PSP.
Now since you have a file that is zipped like your normal snes games, copy the file to a folder in your Snes rom directory called music. Then run the snes emu of choice and and pick that file. You will see a screen popup and display the Song, Game, Artist, dumper of the audio track.

I have tested this with the SnesTYL emulator. There is a big difference when sound quality is below 44k ... so I would not recommend listening lower then the 44k setting.
I have noticed that I get the best and most natural sounding playback when the emu is set to:
Frequency : 44khz
GFX engine : Accurate Software
Speed limit : on or off [you may notice a small difference]
CPU Clock : 333
Recap : Why does this rock?
Extremely small filesize
High quality 44khz playback
Classic Snes Video Game Music (with perfect playback)
Takes only a few minutes to make the files