So I just finished that chapter for the second time. To refresh your memory, it's the one right after Emmeryn dies, where you face the pacifist Plegian general Mustafa. The music is a perfect mixture of sadness and hope, really fits the moment.
All of the other non event songs can be chosen to play during risen skirmishes once theyre unlocked, but as far as I know, this one only plays at that part. Vote in the poll and discuss.