Hey, have you figured how to record voice separately? Maybe try to look in the manual for the solution (they have tutorials on the website)
I have a trial version of the software and didn't have enough time to check all the features, but there's in the "speaker icon section" a button "multi-channel audio recording" have you tried to use it?
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*edit*
I figured it out!
Try to turn off the mic in settings of recording video. Press F9(hotkey for recording video) and F10 (hotkey for recording audio). My friend told me he records his videos like this. I don't have mic to test this. Write if it works for you, I'm curious.