Multicam confusion

Ok here we go:

New fcp x user... Vet 7 user

2 source cams , 5d, 7d, plus 3 other tracks of audio ( shown as one audio clip ("3" on FCPx timeline). All syncs up, cuts nicely. I am able to select Audio 3 as the full time audio in the multiclip cut.

My issue is audio. I (mainly) want to use one of the extra audio tracks as the master audio.

I tried "opening up" the multiclip, to try to set which audio I'm hearing. ( turning off some tracks, disabling, or pulling volume down), but when I go back to the multiclip, the mix is different?

I admittedly have a bunch to learn in X, but right now I'm a bit deep. Can anyone help? anyone willing to take a few minute phone call? ( considering it was impossible to even state the QUESTION clearly....)

Thanks

Paul