The 'best' way is the SMM (Safety Manager Module), it is a UCN communication card that resides in the Triconex rack that is similar to the LMM. It allows the Triconex PLC to be a UCN node. It's supported in R500 and above LCN revisions. We were at revision R400 when we installed Triconex turbine controls, so we used the APM serial interface with modbus protocol to communicate, our critical controls are hard-wired from APM I/O to Triconex I/O.
The Safey Manager Module (SMM) is proven, but getting $$ as Honeywell is pushing vendors such as Triconex to OPC and Experion (Same applies to Hiway interface modules - HIM). Triconex has an embedded OPC server module as well as external OPC servers from Matrikon and Software Toolbox.
Of course, Modbus via EPLCG, etc. would be the least expensive and also proven approach.
So basically you are saying the Tricon HIM 4509 will work with the TDC3000 just that there are other options that are now more common to be used for the communication link.
Would like a confirmation from Honeywell side but with no luck. Triconex confirmed HIM4509 is fully tested and supported.