Gain Balance

The Zoom H4n was not very friendly for connecting to mixers. It wouldn't properly detect the signal from the mixer, and so you would have to reduce the mixer's output and drop the H4n's input all the way down to 1 out of 100. The H6 has greatly improved this.

With the pad switches off (set to 0), setting the gain knobs to around 2 is probably enough if your mixer's outputs are at 0 (sometimes called “unity”). If it's easier for you to keep the gain knobs near the same level you might use with microphones, consider switching the pad on, which will drop the input signal by 20 dB. That's also possible with the EXH-6 XLR/TRS capsule, but there is no pad switch for the 3.5 mm input on the X/Y capsule.

Keep the mixer's output at or below 0 and reduce the H6's input. That's generally better than increasing the H6's input to boost an incoming signal. But if that's what you have to do because of limitations with your setup, it's acceptable and won't corrupt your audio.

When looking for the ideal input gain on the H6, send some test audio through your mixer. That could be talking into the microphone or playing back some audio. Only ensure the samples are a good representation of your actual recording levels. So try laughing, playing sound clips, and getting excited. Adjust the gain so that the average audio is between -12 and -6 on the H6, and that it never jumps all the way up and causes the track lights to blink, which indicates clipping and distortion.