These are duels (PvP), where the Barbarians fight it out 1 vs. 1 with the Full IK set. It's a rather interesting duel, as your Whirlwind skill and PvP practices do come to a test. The biggest problem is the attack rating of IK Barbarians, as they usually have more defense and less attack rating. So the Angelic ring and amulet combo can be really useful here - to get a thousand more attack rating up. You could also use a Metalgrid though.
The other factor is sockets. The IK weapon is usually set up with ias/ed/ar jewels, but for armors in my opinion the Ber runes (8% damage reduction / rune) are the most useful, as they add up to 24% of damage reduction on the character (for a total of 44% with complete set). You can tank more hits, and the IK set can already tank more than a few. In fact a duel can take a while, if you both play defensively.
I recommend you try to figure out where your opponent is going, and Clip whirl them (away or from the side), or try to whirl into his whirl (a more offensive approach). Keep in mind the hammer range is low, so skimming doesn't work too well.
If they try to desync by stacking increased speed items and charms, try to whirl ahead of where you see them on the minimap - you just might get a lucky shot. Also if you can, agree to no more than 4 mana potions for one fight (4 because nobody can prove the last slots are really empty). Also speaking of Demon Limb and other precast items - I consider them bad mannered in this duel, because your skill and equipment tweakage should be the deciding factor here, and not the depth of one's stash.