I've come up with "theme" soundtracks to each species for my campaign.
Terran-Shivan Alliance: I need a "heroic" tune for this, since they are the good guys in my campaign after all. I chose the ITF 1 soundtrack from The Babylon Project.
Vasudans: I needed a "Vasudan" yet menacing feel, since the Vasudans were the arch-enemy of the TSA.
Ambience: FS1 m5_nrml1
Battle 1: FS1 m4_bttl1
Battle 2: FS1 m5_bttl1
GTVA (Terran) and EA: Brassy, militaristic, "army music". The "2R" soundtrack that was in the Inferno VP but not used in the campaign worked perfectly.
Combined GTVA: For a blend of Terran and Vasudan, I'll the FS1 mission 3 soundtrack also found in the FS1 demo. It's some of my all-time favorite music.
Bosch/Gargant: For an evil madman in a nigh-unstoppable ship (the Gargant), you need evil music. Soundtrack #2, "Into the Fire", from The Babylon Project is fine.
Ancients: Rock/Techno stuff.
Ambience: TBP ITF 6 ambience
Battle 1: Hidden battle 1 (Inferno/Hidden Terror)
Battle 2: Hidden battle 2 (Inferno/Hidden Terror)