When I though I might have found a workaround as I recovered the microphone that came with the old Blue & White Apple CRT display… and it doesn't work with the Mac Pro, neither does with the MDD G4, it just happens to work with the Yosemite G3 Power Mac. Albeit I have near to zero knowledge when it comes to this kind of audio stuff, I find it slightly silly, the audio input couldn't be more standard… or am I mistaken?.