Battles

Destroyer Armor is Asgardian, so kinda doubt that. Tony is best with prep if he knows what he's up again. Thorbuster armor was a crapshot and Hulkbuster never did get the job done. As strong as his larger armors are, they don't have the speed to be of any help against Dante. His most powerful form is Sparda Dante. Which, if you gave that to him now, would make him ridiculously powerful. He put down Cid with the power of Abigail, equivalent to that of Mundus, without transforming as far as he saw. When Dante first faced Mundus, he needed the Sparda Sword to face him. Dante is so powerful now he doesn't even need it to be at that level.
 
This is one kind of battle Tony Stark generally hates. Because he's going against someone with demonic power/magic. Stark hates magic. It's one of the few things he can't grasp or understand. Generally when dealing with a magical problem, he calls in Doc Strange or some other magic user. However, since he can't bring in outside help, he has to find a means of winning via his technology and resources.
 
As the op has changed Tony's prep to 2 days, that's two days of trying to first compile all the information about Dante he can and then trying to formulate a means by which to beat him. Much of Dante's past and early life is left completely in the dark. Before he opened "Devil May Cry" he worked as a "Hired Hand" solving problems with thugs, gangs and other big bads in the underworld. At that time he went by the name of Tony. After certain events he abandoned that life and began using the name Dante (which may be his birthname given by his mother and Sparda) and started up his demon-hunting/jack-of-all-trades business called "Devil May Cry". If the shabby place (or the anime) was any indication, he doesn't get many clients and he's almost perpetually in debt. Oh and his favorite food is strawberry sundaes. Pizza is his 2nd favorite.
 
Tony only has two real weaknesses as Iron-Man. His ego and the suits power supply. Tony can use too much power and leave him almost defenseless if he's not careful in how he fights. The armor also isn't unbreakable. While very durable, it can be damaged and even taken apart. And to make matters worse here, if Dante has full access to all his powers, that includes Quicksilver. Which means he can stop time.
 
Ah, the old days of PS2. Dante takes on Mundus
     And here, another lord of the Underworld. Dante puts down Argosax in his greatest form, Despair Embodied. Then pulls a Ghost Rider and rides to Hell on his hog.
    And never forget the anime. Taking out Abigail/Cid.
  

Honestly I don't know. I'd say his best bet is having a device made to create a temporary rift into the Negative Zone and BFR Dante. Since morals are on, they won't try and kill each other. So it comes down to restraining the other or debilitating them. Dante has near endless regeneration and nothing can really hold him. Maybe Tony could try chemical darts to try and put Dante to sleep, but unsure if such a thing would work.