If you're handy with a soldering iron you can add an extra MIDI out on your midibox if you just really gotta have it.
Take a MIDI jack and trim the leads on the bottom so there are no thru-hole leads sticking out like I have started here:
Then insulate the bottom with electrical tape or Kapton tape
This is your new MIDI jack
Pin 5 goes through the new resistor to the left side of H16
The +5v is where you connect the resistor on pin 4 to the left side of H15
Ground is connected to ground on the existing midi thru/out ground pin.
Here's what it will look like (sort of. this is a midibox2 so you'll be making slightly different connections.)
(Sorry, I didn't have any 220 resistors handy so I had to use two and it's kind of ugly)
I recommend using wires on one end of the resistors to make it easier to get back into the enclosure.
Drill a hole in the enclosure, leaving enough room for the power jack and the 1/4" jack.
Epoxy the new MIDI jack to the enclosure
Make sure you properly insulate, screw the back plate on and you're done!
To check your work, download MIDI-OX.
It is a fantastic tool to see whats happening and to troubleshoot issues with.
It makes it easy to make sure you are sending what you think you are sending.
Oh and it's free!