RS-232 sometimes runs over 3 pins on a stereo plug/jack. Lots of equipment have started using this connectivity method. I have a Bryston BDA-3 DAC that does just this. The older BDA-2 model used DB9 connectors and the newest model changed to a stereo jack.

However, the Pronto RFX9X00 extender mini-jacks are for IR only.

With regard to LowPro's comments, provided that all 7 components use a different IR codeset, you'd be good with a single extender.

An example of 2 components using the same codeset, consider that you have 2 Sony Blu Ray Players and they do not have a method to select Codeset 1 vs Codeset 2, etc. In this case, you could put Blu Ray Player #1 on an emitter off port #1 of the RFX9400 and Blu Ray Player #2 on an emitter off another port (#2, #3, or #4) and send commands to a specific port based on settings in PEP2.