I don't use spotify, but I am a little familiar with the USB setting thing because of recent troubleshooting I went through. My device has 3 USB modes to choose from. Go into "Settings" on your SGP, choose "Wireless and Network", choose "USB Settings" and you should have 3 choices: "Samsung Kies", "Media Player", and "Mass Storage". Hopefully your app (spotify) can instruct you which one to choose.
I know this doesn’t answer your question specifically, but if you didn’t know how to change the settings, this may help.