I captured a ton of clips as 4 mono audio tracks and there seems to be lots of hiss when the volume is boosted all the way up. Would there be a difference if these clips were captured as 2 stereo tracks? Is it too late to change these 4 mono tracks to 2 stereo tracks after capture and edit? I tried to "pair stereo" but FCP will not let me select it.
What is on the four tracks? You might have tracks with no audio so just mixing them all together is introducing hiss. makes no difference if they are stereo linked as that just changes the panning which is wrong if the source isn't stereo.
It won't make any difference to the amount of hiss whether you import as mono or stereo. I'd be inclined to listen to each track individually to see whether the hiss is on all the tracks or whether one or more tracks are worse than the others (in which case only use/ boost the cleaner ones).