Loud hum and buzz... I think I know why but I don't know how to solve
The TEA2025 is designed for single supply operation only, and has internal components connected its ground pins which will be referenced to the negative rail when powered by a split supply. 

The MAX359 only draws 200uA from its negative supply, so I suggest you forget about trying to create a virtual ground and use a negative voltage converter (eg. ICL7660) instead. The LM317 can then provide a regulated voltage of 6 to 9V, to power the voltage converter and switching control circuit.