Yes, you'll still need KB protection. If I recall, Fire Armor gets a meanly 1 KB protection in temperature protection, meaning you will avoid knock down, but will still get thrown around a lot.
I've been enjoying my Fire/Fire tank lately, i don't currently have an APP on him, but plan on respeccing into Soul for Darkest Night.
As the others have said, go Fire if you want more AOE focus, go Energy for more ST focus.