I have an IRTrans Ethernet with the optional 2nd IR output. Each of the outputs are connected to my Xantech ZC21 connection block via an opto-coupler. It works perfectly. The couplers I have are IRLincs from Smarthome (http://www.smarthome.com/8175/IR-Linc-for-Hardwired-IR-Distribution-Systems/p.aspx). These are discontinued now but pop up on eBay from time to time. The GC-CGX from Global Cache (http://www.smarthome.com/8124/IR-Converter-GC100-To-Xantech/p.aspx) should work just fine too, although I haven't tried one personally.
-David