Set the Rode VideoMic at the 6D and the GoPro 3+ Silver with USB adapter, class sound now in both devices. When 6D you should turn down the input level in the menu, at the GoPro this was the hardware side, of course, not possible, but the noise also bearable. Remedy creates an external audio recorder (Zoom H1) represents a real killer combination in connection with the Rode directional microphone and should satisfy even the most demanding ears. Furthermore then variably placeable. The only drawback I've found so far is the susceptibility to radio waves, since I both cameras (GoPro / Eos6D) like via WiFi remotely steer hear now and then a more or less loud thick thick thick. According to research culprit is the cable (mini) XLR would there be better, but I do not want. Remedy here also creates the Zoom H1 acts as an external recorder.