I am new here, just saw this post and wanted to share how to add own sound:
(1)Went to PAS root dir, in my case for Win 7 (C:\Users\my_pc_name\Downloads\PlatinumArtsSandbox2.8\packages\music)
(2)Made a note of the list of tracks from this directory, you will need to rename your MP3s to match the list
(3)followed instructions at the bottom of this URL, you need 'The more advanced way to add music...' (http://www.sandboxgamemaker.com/wiki/in ... to_Sandbox
(4)Downloaded Audacity as said from above URL, to convert files to ogg file types
(5)Made a copy of the original PAS audio files, added to new (TEST) folder in the same directory
(6)In Audacity, you will need to Export, not Save as... (choose OGG extension)
(7)Simply copy your ogg files, accurately renamed, as Agent, Jingle, and so on...
Start Sandbox... remember PAS runs these @ random;-)
Have a great week!