Marc B., look at AkComponent.cpp for a workaround...
if you need to call a Blueprint function, you can use PostAkEventByName(), which calls PostAkEventByNameWithCallback() with the appropriate default/null args...
int32 UAkComponent::PostAkEventByName(const FString& in_EventName)
From cpp, you can call PostAkEventByNameWithCallback directly with the default/null args specified here in comments, if you want...
AkPlayingID UAkComponent::PostAkEventByNameWithCallback(const FString& in_EventName, AkUInt32 in_uFlags /*= 0*/, AkCallbackFunc in_pfnUserCallback /*= NULL*/, void * in_pUserCookie /*= NULL*/)
Whatever works for you. All roads eventually lead to AudioDevice->PostEvent().
- cheers