ID'ing 5.1 channels; creating quad mix from 5.1?

I’m a newbie at the multi-channel thing. When you open a 5.1 file in Audacity, is there a fixed order to the channels? In the screenshot of the track I’ve opened, the front channels are obviously the first two (it’s a stereo pair), as is the low-frequency effects channel (#4).
But which one is the centre channel? Is it always in the same order in Audacity? Why did the front channel show up as a stereo pair, but not the surround channels?
Also, I’m basically trying to create an old-school quad mix from the six channels. How would the centre channel fit into this mix? Would it be mixed with the front channels, the surround channels, or both?
Thanks!
Using Mojave 10.14.6, Audacity 2.3.2.
Screen Shot 2019-12-08 at 10.12.03 AM.jpg

Yes and no.

Yes:

The tracks are always in the order:
| Channel 1
| Channel 2
Channel 3
Channel 4
Channel 5

Where channels 1 and 2 are imported as a stereo track, and the other three as mono tracks.

No:

The “mapping” of channels to speakers depends on the file format. Some typical mapping assignments are listed on Wikipedia: Surround sound - Wikipedia

I’m not super-clear after looking at the Wikipedia page. I’m guessing the centre channel in my screenshot is the third track down.
But how would that centre channel figure into a quad mix — i.e., would it be mixed with the front channels, the surrounds, both, or none?

[u]This page[/u] has downmix tables. The center should be mixed-into the front channels at -3dB.

Mixing increases the levels so watch out for clipping and reduce all of the levels proportionally before mixing, if necessary.

The “point one” LFE channel is for low frequency effects and it should not be used in a 4.0 downmix. (The other channels contain “regular bass” so you’re not throwing-away any regular bass.)