Separating L/R audio pairs (specifically mic inputs)

I'm making something like a "Karaoke Singing Game" that needs to be "extensible" so, (within reason,) as many users can play as the user has audio pro audio inputs (eg: from the Focusrite or M-Audio interfaces) into which to plug their microphones.

I've got the nuts-and-bolts of pitch detection and scoring/display sorted... but...

The problem I'm running into is that I have not been able to find any successful reference to separate Line1 (L) and Line2 (R) of my M-AUDIO interface into separate mono channels in Unity. (Unity seems to be combining mic input from M-Audio's inputs 1 & 2 (1/2 L/R pair) into one, [mono(?)] channel: ...my tests show IDENTICAL results when plugging my mic into EITHER Line1 (L) or Line2(R) inputs on the M-AUDIO interface.)

(I've used the M-AUDIO interface for years to record separate mono audio streams simultaneously into my Digital Audio Workstation, so I know the problem isn't with the audio interface.)

Any ideas, thoughts, leads, or suggestions would be greatly appreciated!

Thanks so much!

~Amadhia

(P.S. I'm running Unity Editor under Windows)