yeah using amp is the key as inject acid will mess you up regardless of resistances if you fight him long enough. You just have to kill him quickly as it is virtually impossible to sustain through inject acid.

"While you are injected by Acid you have -8000 regen, but it only lasts about a second or so. " -Game from a comment on the acid injector on the wiki.

Basically it proves my point. If you get "injected," you are probably going to die even with maxed resists. The ctc on acid injector suggests that "inject acid" is a curse and thus only effected by curse reduction on things like fade and cleansing aura. Confirm that with someone more knowledgable though as I am not positive on that detail. My zon that wears puris (cleansing aura) doesnt usually get affected too much by inject acid so I suspect that I am correct.