1) A couple of things to keep in mind, any modifications that you do to these emitters will slightly change their electrical characteristics. If you are making comparisons of how well the control systems transmit learned commands, then your judgements may be slightlye skewed by demultiplexing multiple IR signals to a single emitter.
2) Also, by using multiple emitters, they will each have different placement on the front panel. Ask any installer and he will tell you that slight placement adjustments are very critical for certain pieces of equipment.
3) If 1 of the systems was feeding back interference (such as a plasma, or lighting) to a component via the emitter, it is possible for it to block out the signals from another system, or even the OEM remote control.
I think that the best solution to eliminate any of the above variables is to have each control system go to a mono-mini female jack (a short misnomered woman that speaks out of only 1 of her 2 faces?) (sorry) for convenience sake or some sort of barrier strip where you can switch between the different systems.
