My 14 yr old DS can't stand his Step brother & my DH can't rise above it

[Subgirl]

I've been with my DH for 5yrs & married for nearly 2. My 14 year old son loves & worships his SD but he cannot stand his step brother who is also 14. The two boys are polar opposites, my DS is political, bright and geeky, my DSS is sporty and delightfully daft but not too clever.
My DH gets furious that my son doesn't like his and can be very angry about it, as a result their relationship has now deteriorated to just ignoring each other. My son is very hurt by this but his teenage perspective means that he won't see that if he could change his attitude to his step brother then my DHs behaviour to him would be better. I am stuck in the middle and my DH seems incapable of rising above it. He is extremely protective of his DS in all things and feels that by being kind to my DS he is somehow condoning the dislike he feels and being disloyal to his own child.
I feel utterly stuck and I don't know how to fix this, I know it's really hard for my DH but I also see my DS suffering from the loss of his relationship with his step dad. I just don't know what to do.