Good evening and thanks to all for the replies. John Roberts actually answered my question. I have built several of these circuits but only used the series resistors and not the shunt resistor and never had any problems. I am getting ready to build another for another project and reviewed the RANE article and also a similar article on the QSC website with circuit attached below to remind myself of the correct value resistors. This is what prompted the question.
Thanks again,
Garry
Keep in mind the diagram you posted is for unbalanced source summing, low impedance balanced line summing would use lower value resistors.