Yeah I'm going to go back to the 3.3k one till I can get a better one.
One more question though, when I use the Atari for input the bits still seem to go as low on the scope as they do for the other MIDI signals that do work. Does this rule out the current being too low from the Atari? Or could a low current cause some change in the rise and fall of the signal that screws with the UART?
Could it be some variation in baud rates that other gear is more lenient with (unlikely I know) or some extra junk data that the Atari's putting out (also probably unlikely).