Honey- this doesnt sound good. I think the Dane was unsocialized enough, and with a dog of that size, I hate to tell you what I think your options are here. Can you return him to Dane rescue?
Your dog is telling him- dont do that- and his response is "THE HECK I WONT- DONT TELL ME" ..
I know you love the new dog, but your other dog deserves not to be terriorized by the new comer. Short of getting a behaviorist ( and the fact he is growling at you- I dont think there is this option) I would return him for peace in your house before someone gets seriously hurt.