Hi - don't know how deep your knowledge is, so I will go into depth:
Basically - if you want to interrupt as much as possible, you need the highest PER you can get and also attack pretty fast.
A PER score of 17 will lead to an interrupt value of 21. If you put PER to 21, it will be 33. That's 30% more. Interrupting Blows adds +15 (like 5 points of PER without the ACC boost).
So you will be at 48. But that'S still not enough to land guaranteed interrupts. The base concentration at RES 10 is 75. You have to overcome concentration with this roll: rollDie(1-100) + 48 > 75. The chances against foes with normal RES are ok, but not overwehleming although you put all you have into PER.
Every point of PER counts now. So you will have to watch out for stuff (items, resting, food, talents) that give you a bonus to PER. Champion's Boon (+10 PER = +30 Interrupt) and Crowns for the Faithful (+6 PER, +25 RES) are great for this!
At the same time you want to lower concentration. That can be done by you (as you said: Threatening Presence is a way to reduce concentration a bit) or by party members. There are some spells or other abilites that reduce concentration directly or indirectly (= -RES). Some are: Expose Vulnerabilites (awesome for a barb, lowers concentration and DR), Miasma of Dull Mindedness (-6 RES means -18 concentration - but the AoE is damn small), Arkemyr's Wondrous Torment (it'S just one foe at a time, but it lasts very long and is good against tough enemies), Painful Interdiction (this stacks with your Threatening Presence - you can use Brute Force then), the lvl-1-Chanter's phrase that reduces concentration by 10 (huge range, no ressources needed).
Then there's a new item, a ploeaxe, that has an aura that causes -30 concentration. That's superawesome - but it's too slow to be you own weapon. However it would be the perfect support weapon for you. Put it on a chanter abd let him sing that "stumbling over words"-phrase and your foes will suffer from -40 concentration. That alone guarantees you 100% interrupt chance against "normal" enemies. For the tougher ones you just can use the things I listed above. With those combined you can interrupt every enemy in the game 100% of the time - you just have to make sure that those debuffs hit. If they don't, your sky high PER (with Champion' Boon and stuff) is still enough to interrupt even the toughest enemy for a good amount of time. So, my party composition would be:
- hearth or wild orlan barb from the White that Wends with 21 PER and high DEX. RES shouldn't bee too low because if you get interrupted you can't interrupt others. Iterrupting Blows, Two Weapon Style, Brute Force, One Stands Alone
- Chanter with that chant (and later that poleaxe)
- Priest with Painful Interdiction
- Wizard with Blast and The Golden Gaze as weapon as well as the spell I mentioned above
- The rest is up to you - a cipher would fit in because he also profits a lot from Threatening Presence + Painful Interdiction. A monk also loves the low fort and will defenses
For you weapons: you said you want to interrupt and also stun. Well there's just one two combos in this game that fit to this:
1: dual wielding the Vile Loner's Lance and Cladhaliath. The Vile Loner's Lance has a very long Interrupt of 1 sec (instead of 0.5) and Cladhaliath can be made so that it causes stun on crit. Vile Loner's Lance also causes -5 defenses on hit - fits perfectly well with the stun-on-crit. Altough this is a nice combo, it looks kind of weird - if you have no problem with that, I would recommend those - because you can get them early.
2.: Then there's Shatterstar (or was it Strike Hard? can't remember) plus Godansthunyr. Those are also great: both have long interrupts (1 sec and 0.75) and other nice enchantments. +1 MIG and stun on crit for example. And the best part: it looks good on a barb! But Godansthunyr comes pretty late.
Another good item for a interrupting barb is Mosquito. That rapier causes interrupts that last for 0.75 and is fast. On top it drains endurance whcih is always cool with carnage. You could combine that with the March Steel Dagger in order to speed up your attack even more - but I think it's not your kind of style for a barb.
You want to attack as fast as you can, so try to stack lots of speed modifiers: Frenzy, Gauntlets of Swift Action, Durgan Refinement on armor and weapons. You can reach 0 recovery with dual wieding and a light armor like padded or hide or even durgan reinforced heavier stuff (but then you can't use Vulnerable Attack):
Frenzy (1.33) * Durgan Refinement weapon 1 (1.15) * Durgan Refinement weapon two (1.15) * Gauntlets (1.15) + Two Weapon Style = 2.22. At 2 you have no recovery - so there's room for either 20% armor-penalty or Vulnerable Attack. I like Vulnerable Attack - so I'd go for the durgan reinforced monk's outfit perhaps (=0% recovery penalty) and pump survival for +2 extra DR and wear a Blunting Belt and drink some potions of Iron Skin in tough fights.
There's also the Helwax Mold: that tiem (from a stronghold quest) lets you duplicate any non-soulbound item. So it would be nice to clone the Vile Loner's Lance or Godansthunyr or whatever weapon you like best for this. Or even that strange poleaxe I mentioned. I don't know if it's aura stacks - but if it does, it would be superaweseome.
I think that's all I have to say...
edit: oh, forgot: if this is set up properly (high INT is also important) it creates a perma-interrupt-lock in an AoE. No foe is immune to interrupts and they also happen on grazes. It's superpowerful even if you don't use ALL the stuff I mentioned above. Just don't get disabled. Suppress Affliction of Liberating Exhortation are your best friends. Ah, and Frighten (chanter phrase or barbs yell) and Terrify (spell, invocation or shout) also lower concentration a bit - as well as keeping you alive by lowering enemies' ACC.
edit2: I just hope the chanter's chant and that poleaxe aura stack - I couldn't test it myself yet, sorry.