So i want to make a sound pack, that will mix the TTS and recorded wav's, is that possible?

I tried this:
CLIENT_SWITCHED_TO_CURRENT_CHANNEL_APPEARS = say("${clientname}") play("switched_tocurrentchannel.wav")

I could not make this work.... Why?

If this is not possible, there is any plugin that would allow this?
And if this is completely impossible, consider this as an feature request!