I think it's amazingly sweet that the name meaning is what is motivating your husband. That seems like ideal ground for finding "THE NAME" that both of you can love. Some more ideas to add to the great suggestions you already have (some pretty unusual, but some more mainstream):
Griffith - strong fighter
Patton - fighter's town
Donahue - dark fighter
Dalibor - far away fight
Donaghy - strong fighter
Viggo - war (there's a fight for you!)
Balendin - strong and brave man
Everado - brave
Enando - bold man
Elonzo - ready for battle
Ruggiero famous warrior/prayed for (depending on which nationality you trace)
Raghnall - strong
Caelan - mighty warrior
Nicholas - people of victory
Ragnar - warrior
Rainier - wise army
Raynor - mighty army
Garrick - mighty warrior
As you can see, there are many names with meanings similar to "fighter" that would be appropriate. You can search for meanings in Nameberry's Super Search found at the top left of your page, and if you're interested in more unusual historic names you can try behindthename.com
About the middles, it's really nice when there are two middle names for those to honor someone from each side of the family.
I like Leo much much better
Love, love, love the suggestions from Saracita. I'm not a huge fan of Leo but I definitely agree that it is better than Caden. I think his reasoning for liking Caden is very sweet, though, and I love the idea of finding other names with similar meaning. I also like the suggestion of Cade. I know a boy named Cade and even though it looks similar on paper, it actually sounds very distinctive from all of the Caden, Brayden, Aidan, Zaden out there. From Saracita's suggestions, my favorites are Griffith, Viggo, and Garrick.
Thanks for the suggestions, and before I considered Leo, Finn was at the top of our list and then good friends went and named their puppy Finn!
Lorcan means little and fierce.
Some names that might be meaningful...
Anders- "warrior" (relatively rare, but I know the cutest boy with this name)
Cadell- "little battle"
Cedric- "war chief"
Duncan- "brown warrior"
Gabriel- "warrior of God"
Gideon- "mighty warrior"
Kane- "little battle"
Killian- "little warrior" (love)
Kyler- "little warrior"
Lewis- "famous warrior"
Nolan- "little champion"
Rainier- "wise warrior"
Names that mean "wished for"/ "waited for":
Reuben "behold, a son"
Samuel- Hannah couldn't have a son... she prayed and got Samuel. His name means "told by God"
Leo, hands down. It's infinitely better than Caden (blegh!!)
There are so many Cadens, Caidens, Caydens, Caidyns, Kadens, etc. in the world already.
Leo is distinctive, timeless, and handsome. Caden is overused and already becoming dated.
You must fight this fight. Leo is infinitely better than Caden. If he can't come around to Leo (which I adore) then come up with a new name. Leo exudes strength and charm, while Caden lacks character. Not a great name, so don't give in!