This is a case of inter-male aggression and some dominance aggression as well and it takes some work but you can train him to not be so aggressive. I would only allow interaction for short periods of time first, so they can slowly get used to each other rather then let the aggression build. Do not use harsh training technics as this will only add to the aggression. You need to start by taking away any treats, toys or favorite furniture, then as he obeys you reward him to show him that nothing in life is free. Reward him for good behavior and ignore him when he is bad if possible. It can take up to eight weeks for him to accept the social structure of his new home. With inter-male aggression is can be common which is why he is more aggressive towards your male dog. You as the owner must establish a strong leadership role over all the dogs in the household. In events where the dog is competing over a resource, which is you, the top ranking dog needs to stay in company with you and remove the subordinate dog. In this case being the new dog. If the fighting is severe then you need to seperate them and them slowly re-introduce them using good training methods. I am going to include a couple of links below for more further information on tips to help curb this aggression that I feel will be very beneficial to you and if you have any further questions please feel free to ask.
For inter-dog aggresion:
http://petplace.netscape.com/articles/artShow.asp?artID=1971
For dominance aggression:
http://petplace.netscape.com/articles/artShow.asp?artID=1984
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