With Avaya, you only need to use the IVR treatment type. Just configure a VDN the same way you do an announcement but have it play music after the adjuncts in the vector. It is important to have your secs of music in the vector longer then the duration defined on the IVR treatment type.
What will happen is, Genesys will queue the call on this RP while there is no agents available and customer will hear music, when the treatment time expires, Genesys will move the call to the next treatment. If an agent comes available Genesys still has control of the call and will route to agent.
Does this make sense or you want me to explain futher?