First of all, the original 6 channel source: are any of those channels cleaner? Secondly, the noise reduction often works best with several "gentle passes". Also, eq can help to remove unwanted noise outside the speaker's range. Adobe Podcast can help, but because it re-synthesizes the voices, things can get weird. And there a number of third party plugins that can help. Waves Clarity, dxRevive, Acon's extact:dialogue, Supertone Clear, Crumplepop Audio denoise. Many of these have trial versions.
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