I've been searching for this, but couldn't find the definitive answer: Does the output jack of the E17 support 4-pin (TRRS) headphone cables (cables with a mic), or do you need a 3-pin (TRS) cable?
My E17 is broken due to accident so I can't answer your question. But a typical (Apple compatible) TRRS plug should work in E17 (as the plug should work almost universally), just that the mic won't work since E17 doesn't have any hardware inside to support mic.