Sorry for the delay. Was out of town. Everything you need should work over the SV network or ethernet, except for devices requiring serial port connections, as Steve noted (you didn't mention any serial devices). One display should be set as master and the other as standby, so the standby display takes over network functions if the master fails. You do not need to splice the audio from both displays. There is no audio input to HDX displays. The only audio output from them is alert audio. Theoretically, splicing both audio outputs together will allow the standby display to still send alert audio if the master display fails. However, having both spliced together during normal operations can sometimes cause an echo effect due to both displays sending out duplicate audio at the same time. So it's your choice as to whether to do that or not.