I’m not sure if the c200 series supports Audible or not. These are ancient and rather low-end players. There were 2 hardware versions like the e200 series. In that series (e200), only the v2 model worked with Audible if I remember correctly. This might also be true of the c200 series. You should check with Audible if this is a supported player or not.
You can find the firmware updates for all Sansa players (including both versions of the c200 series) in the Sansa Firmware Thread.
