So, I set routes on anveodirect that support T38, and so far so good!
One question I do have is why I can't send T38 to T38. When I force the Cisco SPA112 on both ends (send and receive) to be T38, it seems the call is never answered (or perhaps never actually made). But when I set defaults, the sending device goes to G711u and that seems to work.
I guess I'm just trying to understand this and get some consistency. Most of my internet searching hasn't been very helpful as there are a lot of T38 haters out there.