Dennis,
We facing similar situation. The I600A/I600 are used for orphans only, US immigration laws have very specific criteria for who can be classified as an orphan.
In general, I've learned that orphan status is granted if: 1) both parents are deceased; or 2) one parent is deceased but surviving parent cannot provide care and has formally relinquished rights to child; or 3) child has been abandoned to an orphanage.
Read about US immigration laws at:
http://www.bcis.gov/graphics/services/index2.htm#app
To find out what Thailand needs in order to allow you to adopt child, go to:
http://travel.state.gov/adoption_thailand.html
Good luck,
-Loc