Reg. the `textmath' option, this is the description from the manual:

    `textmath' will make all text math subject to previews.  Since math
      mode is used throughly inside of LaTeX even for other purposes,
      this works by redefining \(, \) and $ and the `math' environment
      (apparently some people use that).  Only occurences of these text
      math delimiters in later loaded packages and in the main document
      will thus be affected.

Best, Arash