Multiple MIDI THRUs (Bypassing Arduino)

I'm trying to have multiple MIDI THRUs split off from a MIDI IN data signal (at the same point where the MIDI data goes into the rx pin). Unfortunately, I have some boards etched already and I'm not getting the expected result from the following circuit:

The idea for this came from:

via: RuggedCircuits in
"Arduino sending MIDI to two devices at the same time?",63681.0.html

Is there a way to slightly modify my circuit to get the job done? Hopefully I can still use the IRLIB9343. I have subsequently found that most MIDI THRU circuits recommend a method involving 7404 HEX INVERTERS and a 5V+ on MIDI pin 4.

What's up with all the grounding on the method I originally chose to go with? Why no 5V+?

I think I have a fundamental lack of knowledge on the subject. Is MIDI protocol inverted binary compared to what an Arduino rx pin expects? Can i route the MIDI IN data from before the opto isolator into my iRLIB9343 THRU setup to avoid using an inverter?