I finally got a legit extension and multi entry from Samut Prakan immigration. In case anyone else has the same problem when ditching the agent route, here are the documents they requested:
1. Copy of TM30 receipt we filled out when I first arrived back from Cambodia.
2. Copy of passport with 1st and current visa and info page.
3. 1900 Baht
4. Copy of wife's ID card
5. Copy of our marriage certificate from the USA (I did the non marriage option, but they still wanted the marriage certificate).
6. Copy of house ownership certificate
7. 4x6 photo
8. Original bank certificate showing bank balance.
9. Copies of all pages from bank book, and this is important, they wanted a transaction on the day of the application. I had one from two days ago, but that was not enough.