Since I'm also not a proponent of letting the smoke out of electronics, let's take a step back and look at what we know.

1) An IR emitter connected to the 970's IR OUT does not deliver IR commands from the 970's sensor to another device's sensor.

2) The 970's IR IN works fine with Xantech IR distribution systems like these connecting blocks.

Based on those two items alone (and reinforced by the information from Steve identifying the 970's IR input/output as a passive design), it seems that the IR ports on the back are effectively independent of the IR sensor on the front. That means that it may be possible to feed a signal into the 970's IR IN and get a copy of that signal back out at the 970's IR OUT, but it appears to not be possible to use the 970's IR sensor as a shared sensor for the entire system. The fact that Elmosaurus's test using an IR emitter connected to the 970's IR OUT failed to provide a copy of the signals received by the 970's sensor is the biggest clue.

I may have just re-stated the obvious, in which case I blame the late hour.