While I really enjoyed the Kane Combat Theme, having it played in battles against Armada Troops in The Machine Core instance, it really gives away the special feeling in battling against a boss that's supposed to have their own combat themes, both unique & shared, that is to say, Kane.
Having his boss combat theme played before battling Kane... that really gives away that special feeling in battling a particular boss. It's like The Rat in W101 Test all over again.
El Kaboing, I highly ask of you to do this request, have the Kane Combat Theme played for battling against Kane only, not before. I really like boss combat themes, yet, that one plays in normal enemies before the boss, & that really gives that special feeling away.
In honesty, I'd rather have boss combat themes, should there be new boss combat themes made, which I really want to hear, played to specific & even shared bosses only, rather than play it for both enemies & bosses, if I were you.
That said, please do this request, so the special feeling in battling Kane with that boss combat theme only will be appropriately preserved & used there.