As I read the rules, parrying multiple attacks by 1 foe (e.g., foe using a two weapon combat style) is quite easy: You get you full DB against both attacks.
Is this correct? So, when I'm the guy with the two weapons, my only advantage is (so to speak) 2 rolls instead of one. That's not too bad, statistically, but I was wondering if I read it correctly.
I'd say you get
most of your DB to each attack against you, but not necessarily all of it.
Quickness Bonus: If you're not aware of the attack, it doesn't make sense to give you this.
Armor Bonus: As long as you're not somehow attacked where the armor doesn't protect (and HARP doesn't use armor by hit location by default), you get this vs. all attacks.
Shield Bonus: If you're attack from the behind, or when you don't have the shield ready, I wouldn't allow you to count its bonus.
Talent Bonus: I guess it's easiest to always include this.
Cover Bonus: The direction of the attack can change this; this is always open to GM adjucation anyway.
Maneuver Bonus: This is the interesting part (the "add OB to DB" part). I would believe you can't just add your OB to all attacks just like that (when you're doing a Full Parry, for instance). Instead you must make a Multiple Parry (another way of saying you must divide up your OB among the parries so that each point of OB can be used only for one parry, not all of them). The sentence "He may parry up to one attacker for every 10 ranks (or portion thereof)" I read only as a limit to the number of attackers you can parry against; not that this combat action is usable against attacks coming from different attackers only. Indeed, with 9 or fewer ranks he can't parry against more than one foe anyway, which I read as actually supporting my interpretation, not the other way round (otherwise you could as well say "you can't use Multiple Parry unless you have 10+ ranks").
So, yes, in a standard combat situation, I'd say you do get your "full" DB against both attacks. Assuming you're not parrying (an important exception) because then you can only add half your DB against each attack.
This makes two attacks pretty nice even though it might not first appear so - assuming you're dangerous enough for the opponent wishing he could do a total defense against your attacks!
(On the other hand, if you can only perform two weak attacks, then you might be better off ditching that two-weapon idea, and concentrating your stuff into a single powerful attack).
I would appreciate anyone pointing out any mistakes in my thinking I have made.