Whilst this doesn't answer your question, there is also a "One way IP strings" (also known as a 'Socket Sample) driver that may be worth looking at instead of using the Two Way driver.
It is available if you log into RTI Forums in the "Unsupported & Third Parties Driver' section.
I've used this driver to control a Media Centre (WMC).
This is the command that I use for 'Play': play\r