@iska The music for Deus Ex and Unreal Tournament was written in Impulse Tracker format, but shipped in the Unreal engine-specific container format UMX. Wikipedia also claims that the first Unreal was like that, but I dunno the actual history. Guess you could find the composers on twitter and ask.

The original notes for the unreal engine only mention IT.

web.archive.org/web/20080820060250/http://unreal.epicgames.com/Music.htm

Looks like it's an involved process, making music for Unreal.

forum.openmpt.org/index.php?topic=4192.0