That depends on what unit #1 is. If it is an Express, then you can use DMX port 2 to string along other devices as port 1 is disabled. If it is anything else, then connecting the Rx module disables the output port and you cannot connect anything else to it. The way around that would be to use a Tx/Rx unit switched to Rx mode which allows you to string multiple devices off of it just like the dongle.