How can extend the cable distance from a condenser microphone to the ADC without loosing fidelity?
I expect you are right about what the wires are.  You should check with a voltmeter though to make sure.  Ground should have the lowest voltage, power the highest, and the return audio somewhere in between although it may be almost the same voltage as the power but at a higher impedance.  If you load the audio line with 10 k&Omega; or so, it should drop a bit whereas the power line should not.

By the way, unless you have specific documentation that says these are condenser microphones, I think they are more likely electret.  However, that doeesn't matter for the purpose of extending the cables.

I would use stereo shielded cable to extend each microphone.  Obviously the shield should be tied to ground.  Since you're only going 8 inches, I don't expect any significant problems with that.  Try to leave as little length as possible for the audio wire outside the shield.