Functional Mock-up Units in the Loop (FMUiL) is an open-source Python package that combines the Functional Mock-up Interface (FMI) and OPC UA standards. It allows co-simulation between software, hardware, and models created with different tools. This paper builds on FMUiL by introducing a set of bridge servers, that link the OPC UA communication layer with various industrial communication protocols. This improvement enables a wide range of external hardware to connect to the co-simulation environment, and allows for comparing communication protocol performance in control applications. In this study, bridge servers are configured for three popular industrial protocols: Modbus RTU, Modbus TCP, and MQTT. To demonstrate its effectiveness, the proposed architecture is validated with a case study that involves a simulated lube-oil cooling system connected to an external discrete-time proportional–integral (PI) controller using each of the supported protocols. The results demonstrate the flexibility of the extended FMUiL framework for hardware-in-the-loop testing, and its potential for broader applications in cyber-physical and industrial automation systems.