Damage Reduction

[draengold]

This is probably been covered before, but I suck at searching for the right terms.

First the General question:
How do the damage reduction feats interact with each other and gear based damage reduction?

Now Specifically:
How do Epic Damage reduction, DD damage reduction and Barbarian damage reduction interact?

If I have epic damage reduction II which gives me 6/- does it give me anything, considering most decent gear is going to get you 10/- pierce, slash and bludge at the very least?

Thanks in advance

[dodrudon]

I don't know exactly how the terms are defined, but it works something like this:

Damage Immunitys are calculated first. They stack from all items, and I'm assuming with DD and Barb class DIs.
Epic Damage Reduction, class-based Damage Reduction (such as DD and Barb) all stack, applying to all three physical damage types. Damage Resistance, which applies to a specific type, such as pierce, stacks with this (of the format 20/- Pierce).
Also, another Damage Resistance or whatever, the ones with +20/10 format, stacks with the aboves.

So:
Damange Immunities all stack, are calculated first
Damage Reductions from class or from feats stack.
Damage Reduction, such as 20/- Pierce, takes the highest value.
Damage Resistance, such as +10/5, takes the highest applicable value.

[mrbadexample]

From what I gather, Damage reduction can stack with damage immunity and damage resistance at the highest value. Now also Dagamre reduction feats from both barb and Dwarven defender to stack with epic damage reductions. This presumably means you could stack the reductions form 2 different classes and epic freats.