Display of TeX notation should be normally set up before worrying about the editor. This is normally handled by filter, the MathJaxloader, TeX notation filters or both, but MathJax can also used with other methods. If the Atto equation editor is working one of the filters is already working.
TinyMCE had the DragMath plugin as a standard plugin from 2.0-2.7, but it is removed in 2.8 because of some license issues. It also requires Java on the client. If you want a tool to help add TeX notation in TinyMCE, you will have to add one in 2.8+. You can reinstall DragMath if that is what you want or use a different tool. WIRIS has plugins for TinyMCE and Atto, but requires a commercial subscription to use in production. Mathslate is a free plugin that works with TinyMCE and Atto.