Other considerations for each jack are listed below. No need to worry about room noise getting into the transmitted signal. TNC output drive level is probably set correctly. If not, it can be adjusted. Probably no narrow receive filters.
Most digital modes use a narrower bandwidth than voice.
With voice filters, there is normally a lot of extra noise received with the digital signal. To get rid of some of the noise, you can use passband tuning or add an external DSP audio filter. If the microphone is connected, room noise may get into the transmitted signal. Some radios may mute the microphone input when the TNC asserts PTT on this connector. TNC output drive level will probably need adjusted.