How about that there are multiple weapons that could complete the set? That would permit different types due to preferences etc. You could perhaps have progression of weapons found at different dungeons that would do different things, but the other components remain the same (armor, cloak, boots(see below), etc.).
DC 14 has a 5% chance of working on a failed roll, unless the scripts are modified. Stun should automatically penetrate mind immune etc. Being stunned during a round is a serious effect cuz you get no attacks or actions. Not happening often makes things more interesting, especially as a hidden effect.
You have to leave the weapon as part of the set or any old weapon would give some pretty overwhelming protection and offense.
I'm not adverse to adding another part to the set:
Juggernaut's Tread (boots)
4 AC
Improved Knockdown
Barbarian Fast Movement
5 Regen
But on to weapons------
Axe of the Barbarian Youth
+6 Enhancement
2d12 Fire
Lvl8 Onhit Effect
Lvl 40 Required
Barbarian Only
In addition to the other set effects -Set effect- Barb Terrifying Rage increase DC+ 5
(none of the barb axes have the crushing damage aura due to aura enhancement of rage)
Axe of the Barbarian Master
+10 enhancement
2d12 fire
Lvl 12 On hit effect
Lvl 52 Required
Barbarian Only
In addition to the other set effects -Set effect- Barb Terrifying Rage increase DC+ 8
Taunt + 5
2d6 Bludgeon
Axe of the Barbarian Lord
+12 enhancement
2d12 Fire
lvl 16 on hit effect
lvl 60 required
Barbarian Only
Str req 22
In addition to the other set effects -Set effect- Barb Terrifying Rage increase DC+ 10
Taunt + 10
Intimidate +8
2d12 Bludgeon
Massive criticals 10
Axe of the Barbarian Hordemaster
+18 enhancement
2d20 fire
lvl 22 on-hit effect
Special required (d15 boss)
Barbarian Only
Str required 28
In addition to the other set effects -Set effect- Barb Terrifying Rage increase DC+ 13
Taunt + 15
Intimidate +12
2d12 Bludgeon
2d20 Slash
Massive criticals 20
A barbarian in this set could probably hang with paladins, and add something to the party. Especially if certain pain in the rear mobs (lil moppets, pitbulls) had about a 30% chance of fleeing in terror with maxed Terrifying Rage. Other mobs such as spiders, abyss knights should be immune. She demons should maybe have like a 10% chance of failure.
Scepter of Knights (This set drops the aura of bludgeon damage)
Heavy Flail
+6 Enhancement
2d12 Cold
Lvl8 Onhit Effect
Lvl 40 Required
Fighter Only
In addition to the other set effects -Set effect- 2d6 Pierce
Scepter of Princes
Heavy Flail
+10 Enhancement
2d12 Cold
Lvl12 Onhit Effect
Lvl 52 Required
Fighter Only
In addition to the other set effects -Set effect- 2d12 Pierce 5 discipline 5 appraise
Scepter of Kings
+12 enhancement
2d12 Cold
lvl 16 on hit effect
lvl 60 required
Fighter only
Str req 22
In addition to the other set effects -Set effect- Manticore Spikes (monster ability from the toolset) 2d12 Pierce to all in radius 10 discipline 10 appraise
Scepter of the Overlord (this set includes the description that the set appears oddly alive and regenerating as if some creature's spirit was active within)
+18 enhancement
2d20 cold
lvl 22 on-hit effect
Special required (d15 boss)
Fighter Only
Str required 28
In addition to the other set effects -Set effect- Manticore Spikes (monster ability from the toolset) 2d20 Pierce to all in radius 10 discipline 10 appraise Pulse Cold Ability (monster ability from the toolset) 2d12 cold
More ideas later