brostenen wrote:So I should not use the 3.3 volt pin on the Arduino MIDI shield then?
Well, it of course depends on the exact wiring of the specific MIDI shield you have, but I can just about guarantee they will use the 5V source and not the 3.3V source, as the MIDI spec is geared to 5V.
brostenen wrote:Basically speaking. I should only use the "TX", "RX", one GND and the 5v pin's on the shield?
(5volt can be sourced from the red wire of a molex plug)
Then I have pretty much just crafted my own kind of butt-ugly and super simple breakout box?
Correct, and the 5V can actually be sourced from the Live! header (pin 1 and 2 on the header pinout you provided) rather than needing to source it from a separate molex connector.
brostenen wrote:I have seen that the Audigy2z has these kind of pin's too.
You are correct, but beyond that, I realized that the pins we are talking about using on the Live! and Audigy headers are actually not all that special for this application... they are exactly the pins presented on every gameport/MIDI DB15 connector. Pin 1 or 8 on the DB15 provides 5V, pin 4 or 5 proves GND, 12 is MIDI OUT (TX on the shield) and pin 15 is MIDI IN (RX on the shield).
Therefore, depending on your comfort level, you could connect the two sound cards just with two Arduino MIDI shields rather than the pre-manufactured cables. As mentioned before, not very aesthetically pleasing, but perfectly functional, and per the MIDI spec.