I was able to finally enable printing in simplify3D directly over a network. The trick was to enable the Telnet capability in DuetWiFi or DuetEthernet. On the windows PC running simplify3D, I used a brilliant little opensource programme called com0com ( link : https://sourceforge.net/projects/com0com) and com2tcp to basically create a virtual USB port on the PC that is linked (wrapping) the Telnet interface on the Duet. Appears the Duet3D Telnet interface supports the RFC2217 extensions. Still testing for reliability etc. but looking promising !!
Would be great if the Simplify3D folks enhanced their MachineControlPanel to support creating such a connection.