Most powerful Pairings?

[Foote]

@Popesixtus

 Is there anything else in the game that gives on-demand DR besides AA's Bulwark?

Hmm. Well, there are a few effects that give temporary reductions, such as Dark Watch Setback's innate power, but it only works for the first attack that would deal damage.

There are some Environment effects that can grant DR as well, such as the Throne Room in the Time Cataclysm. 

[Ameena]

There's also the Biomemetic Plasma Vats. Technically Twist counts too, though only for the damage from a single target...