Party-Line: Combining the announce output from multiple PL stations

Question:  We are trying to use the Announce feature and need some guidance.  We currently have a MS-702 and
two RM-702 stations in our system.  We have a speaker plugged into the announce output of the MS-702 and it
functions when the announce button is used but we would like to be able to use the announce button on the RM-702
to output through the same speaker so we can announce from any of the 3 stations.  Is this possible and if so, how?

Answer:  In order to combine the announce outputs on the one MS-702 and two RM-702s you will need to do this
externally with some 3rd party hardware.  The balanced line level announce outputs on the CC party-line stations are
only routed to the rear panel 3-pin XLR on the MS-702 and the rear panel DB-15F connector on the RM-702.  
There is a company called Radio Design Labs that makes a lot of small line level mixers  and this would be the best way
to combine the announce outputs into one common announce output from all three units.  
Here is a link to their site and one possible solution:  http://www.rdlnet.com/product.php?page=85#!prettyPhoto