Using a PSP remote port and homebrew on the console to change songs etc

[webphreak]

Ok, here goes:
I have just found out that my headunit (Pioneer DEH-P4650MP) can have RCA/mp3 player input and was thinking about how i could get it to send out commands. So that brings me here. I need to know if its possible to download the disk change commands in a raw format and have them readable, and/or if there are distinct commands that could be recognised indivdually. I'm thinking of incorperating this with a homebrew project for the PSP I'm planning and it would rock.

If anyone has any details on how I could do this could they please email me at: webphreak [AT] ihug [DOT] co [DOT] nz
Please excuse me using that email format but it stops me getting spam emails from web scanners.

Cheers,
Webphreak