I’m currently setting up a Pi to test audio and am having some trouble! Too soon to call it now, but did you use the very latest release of Raspbian?
Edit: False alarm, I’d borked something up and I have no idea what. A fresh image has audio working for me.
P.S. have you tried the beta Pirate Radio firmware? It should eliminate any chance of software from the equation. You can find it here: PiratePython - Pirate Radio