I know we can have a ring scanner on one connector and a headset on the other, but I doubt that 2 audio outputs will work at same time.  You can try it, though.  But why don't they use the "Y" cable?  It was made to connect 2 headsets to a terminal, so one headset could be an external speaker instead.  Requires interface to the QD we use, but that's probably easier for them to do than come up with a WT4090 connector to a speaker.