The music playing when Worf is practicing his combat moves is from the opera Les Troyens by Hector Berlioz (specifically Act V, No. 38 - "Vallon Sonore"). It's is the same opera Picard is listening to in his ready room at the beginning of the film Star Trek: First Contact (1996).
Thomas Dekker (Titus Rikka) makes his third appearance in the Star Trek franchise. He had previously appeared in Star Trek: Generations (1994) as Thomas Picard, one of Picard's children in the Nexus. He also appeared as Henry Burleigh, a character in Captain Janeway's favorite holodeck program in Learning Curve (1995) & Persistence of Vision (1995).
As the Titan goes deeper into the nebula, followed by Vadic, a few bars of music from Star Trek II: The Wrath of Khan (1982) can be heard. The last act of this movie famously featured a starship battle in a nebula, to which this alludes.