Eigeny,
I understand your text, but I can't make out what your circuit is. Circuit representations are horribly limited when we try to turn them into text, but

could you add the labels (ground), (tip), and (ring) where you mean them to be in your message?

I take it you are saying that the remote extender does not have simply ground and signal as tip and ring. Okay. Understood. But your text does not mention that the 9 volt output has a resistor in series with it, and it will therefore be reduced to a lower actual voltage when the LED is in the circuit.

Now, since that is the case, it could be that putting a couple of the extender outputs in parallel could effectively lower the series resistance, thus allowing enough current at a high enough voltage to, for instance, be able to go through a Xantech 789 distribution block.

Yes, we need signal plus ground to run Xantech stuff, but we are not going inside the extender to find its actual ground, then connecting that to the Xantech bus, then hoping the output will work -- instead, we have a plus and minus, which could be the signal and ground, respectively, if they are of the proper polarity, voltage and current, to go through a distribution block. Remember, too, that "ground" is a relative term and until you tie together the grounds of two devices, "ground" means nothing. Otherwise, since the big flat end of D cells could be called the "ground," you could not stack them in series to light a flashlight with more than 1.5 volts!

And if the output is as you say, I am back to my original question -- does anybody know what to do to it to make it run Xantech devices? I once needed two different bus outputs from a Niles IR box, and I was able to make a second one out of a high level IR output with a couple of resistors creating a ground reference for the IR signal (the Niles box's IR outputs did not connect either terminal to the Niles signal ground, so this could not be used as a bus either).