The game's soundtrack was created by composers Gordy Haab and the two-man team Finishing Move (Brian Lee White and Brian Trifon), working with Halo Wars 2's audio director Paul Lipson. The first track is called "Run Little Demons". Here's a description from the composing team which also offers some clues into the game's campaign:
Atriox and the banished are a dark, gritty and powerful enemy, arguably one of the toughest opponents the UNSC has encountered to date - and they are also a very intelligent and nuanced group. We wanted to craft a sound scape that captured the raw power and brutality of the banished warlords, while simultaneously underscoring their complexities with beautiful orchestral details and bespoke musical sound design. In this specific cue, we use powerful tribal drums and high tech electronic percussion to create an intense rhythmic foundation. Heavy brass and layered synths augment the rhythm with explosive stabs, expressing dread and fear, while strings add tension and color to create contrast.
The second track is called "Isabel's Awakening", which is also described by the composers:
Isabel enters the Halo universe in a time of turmoil and loss and needs to quickly step up to some overwhelming challenges. We wanted her theme to portray all of this in a musically poetic way. So "Isabel's Awakening" is comprised of three sections: First, an introduction and delicate statement of her main melodic theme. Next, a lament to honor fallen heroes and to underscore the present strife and unrest. Then finally, a reprise of her main theme that blossoms and grows into a bold and hopeful hero's song.
Xbox Wire also has posted an interview with the Halo Wars 2 soundtrack team, where they go into more detail on how they crafted the music for the game. Halo Wars 2 is due for release on Feb. 21, 2017 for $59.99, Microsoft will also release an Ultimate Edition of the game that will include access to the Halo Wars 2 Season Pass worth of content, along with Halo Wars: Definitive Edition, an Xbox One and Windows 10 version of the first game in the series, for $79.99.