ep999-000.rmdp - 52.7 GB
not included

This didn't work for me too. I used winrar and divided it in 1GB part to be able to write it on DVD and it's result was about 36GB and that's good. I'm sure the problem is the fifty GB file of the game.
I'm waiting to see a working conversion method for this game. I really appreciate your hard work.

Personally, didn't understand why UltraARC was not able to split the file correctly!!
Process stopped at.... but not finished.
Should ask Razor12911 about that issue!!

have messaged Razor12911 about that issue, will have to wait for reply.

I downloaded the game via the Store. How can I reinstall it from this backup and trick the Store into not downloading the whole game again?

Just follow the steps listed in the thread:)
Game latest update "quantum.break.patch.to.v1.7.0.0." just came out, so don't forget to apply it before launching conversion.

Try using 7-Zip method instead of Freearc.
Otherwise, I don't think there should be a problem if UltraARC worked on Far Cry 4, There was a 5GB file on that game, which makes it clear that it shouldn't be a problem to work on the 52.7GB file, if Cardinals were used in the program because they have a limit of 4GB, and UA worked on FC4 and there was a 5GB file it means Int64 was used and those have a limit of 9,223,372,036,854,775,808 bytes = 8 exabytes, I really planned ahead.

start the game in the start menu (Windows) not in the game root

i use 7-zip in compression

thank pakrat2k2 for setting

edit ultraarc.ini & set
[7-Zip]
Method=7z
Level=ultra

it finish with 8DVD5

DVD 1 to DVD 7 size 4.37 GB

DVD 8 size 4.14 GB

but i not test because i dont have video card support DirectX 12

That's what I said earlier. Game compression should end up in 8 DVD's.
Thanks a lot wit:)

I tried to edit UltraARC.ini to split it into DVD9, but ran into ISDone.dll error while installing. Do I have to edit records.ini inside QB_1 too?

NEVER touch records.ini generated by UltraArc. IF you wanted DVD9 then should have edited ultraarc.ini for that size BEFORE compressing game. You cant switch after doing the conversion.

using 7z method failed to compress right off the bat. Memory allocation or something?

^^ make sure to also remove the Filename extension from the ini file as well. Leaving at cab/bin is fine for freearc, but not for 7z.