If your psyker is great at neutralising sane opponents with guns, try crazy people with no guns!
In all seriousness, If the PC's are abnormally good against particular foes, then use different antogonists. a horde of frenzied mutants with improvised weapons is actually pretty dangerous.
I ran a oneshot of Edge of Emprie last night. The narrative dice are just amazing, they are incredibly easy to use and after
about 3 or 4 rolls everyone understood how to read them and were adding their own narrative to the game.
I had a single roll determine the outcome of a high stakes Pazaak game. There was enough information in a single dice roll for a detailed description of a complex outcome game (PC's won, pissed off a wookie who swore vengeance against them and got a Hutt lord arrested by an Imperial agent). Compared to what I would get from the dice in DH, its just a different class altogether. I might have made up the same story, but it wouldn't have been aided by the dice, beside the 'won the tournament or not' aspect.
Next time I run Dark Heresy, it will be with EoTE dice and system. it's just that much better.