Due to data communications and transferring power to the iOS device, the cable length is limited. However, you can use iTestMic with our AudioTools Wireless app for remotely sending microphone audio to AudioTools running on another iOS device.
For less than the cost of a quality microphone cable, you can move iTestMic away from the device running AudioTools, for true wireless operation.
We do find that Lightning extender cables work fine. We have tested a 2m (6′) extender and found that performance did not degrade.