While a dual connection is technically possible, our cable does not allow for an external access to the serial data. It was designed to be an easy-to-use plug-and-play cable specifically for the XRX and Garmin 396/496/495. This does not mean, however, that a cable couldn't be made. We sell the Garmin connector to bare wires, and the XRX power/data to bare wires connectors, which could be made into a cable to do as you suggest. The connections are 3-wire simple... power, shared ground, and data (RS232).