I thought I had a good answer, but after reading the "exact quotes" I have to go back through my books to find something more accurate for you.
- Passive DB is always on. No matter what. +5 armour is +5 armour no matter how many people hit it. It's not +5 for the 1st attacker than +0 for all following attacks. You can't turn off passive bonuses and you can't split it by telling your armour to only protect you for 3 points on this hit, then protect you for 2 points on the next hit.
- Parry is split between attackers and you have to declare that you will be parrying 1,2, 3, etc and the single OB gets divvied between the number of attacks, then add the passive (+5) bonus to each.
100 OB wearing +5 Magical armour , no shield
Parry 30 + 40 + 30
DB = 35 , 45 , 35.
- I always took shield to be part of passive defense, unless you block the 1st attacker, then throw your shield on the ground for all the other attacks... That shield is still on your person providing some sort of defense even if you are not "actively blocking a strike.... the opponent still has to work around that shield just being in the way.
- Stunned unable to parry, you only get the passive DB since, again, it can't be turned off. +5 armour still protects at +5.