Greg, you're right, I misspelled it. Mingmen is Du4, and considered the point of the yang of the kidney,which is also used for ki. Yaoyangguan is Du3, but not used for much in martial arts.
In daoism, menming is used as a dantian, but placed about an inch inside the body, not the same place as acupuncture, for the most power. Many chinese styles, including many taiji styles, use this, instead of the point of original chi, for their power point.
I am with you on your points and what you are saying - In Aikido, center, or Tohei's one point, is below the naval and in as you described - but dantian is different, and there are more that one dantian point in the Chinese stuff as you have said.