3rd part of the OST just got released, still not that epic song at the ending of the first few eps... Still. If anyone finds it, please link it here!
Park Do Joon - Burn (AML OST part 3)
https://www.youtube.com/watch?v=6zBOO2xwuT4
First two parts:
Yoon Do Hyun - What the Ggang (AML OST Part 1)
https://www.youtube.com/watch?v=BMU89e8dhp4
Sonnet I - Bring it On (AML OST Part 2)
https://www.youtube.com/watch?v=apv053XagsI
The one still unreleased is this one:
https://www.youtube.com/watch?v=jZPACXSU4FQ
Also, the BGM theme is definitely a variation on "Jupiter" from "Planets" by Gustav Holst - the most similar part starts around min 3. (That suite is so well loved, lots of good composers were inspired by it. Just listen to "Mars"and then compare it with John Williams' "Binary Sunset" theme in Star Wars, for example.)
https://www.youtube.com/watch?v=Gu77Vtja30c