Audio Setting Questions

I have a few somewhat general questions regarding the audio settings under System > Audio. In case it matters, I’m using Krypton on a Shield TV (2015) > HDMI > Onkyo TX-SR607 > HDMI > TV.

1) I haven’t been able to find a good explanation for the ‘Audio output configuration’ setting (Fixed / Optimized / Best match). I’ve seen multiple posts and websites that recommend which setting to use (usually best match), and I’ve seen an explanation or two of the settings and what they do, but I’ve not seen anything in layman’s terms that I can really make good sense of it, at least to the point of being able to decide for myself which setting to use. If somebody could at least tell me if best match is the best to use, and ideally why, that would be great, though I’d really like to be able to understand them better.

2) What does the ‘Send low volume noise’ setting do? I assume it’s associated with the ‘Keep audio device alive’ setting and is a way to perform that function, but I can’t find any info on this setting anywhere. Also, I assume the keep alive setting is to prevent the AVR from sleeping and causing a delay when resuming playback due to it taking a while to detect the stream, in which case I’ve only had issues with this in the past when bitstreaming, not when having an external device perform the decoding, which would seem to imply these settings are only applicable when using passthrough. Is that correct?

3) Why are the number of channels supposed to be set to 2.0 for pass through, since passing it through shouldn’t depend on any such settings in Kodi but rather be dependent solely on the receiver and its settings? I see this recommended not only for Kodi but for Windows as well, and I’ve never understood or seen an explanation why.