Let me suggest new telepathic abilities for Psyker. They can be fitted into current class, without creating a new one.
Psi-field - all enemies in a small area in front of Psyker are being affected with fear and anguish - they start to cry, weep (there are already such sounds ingame), leave bloody furrows on their own faces with their nails. Lasts for 6 seconds, cooldown 120 seconds.
Warp-deception - a chosen enemy starts to attack his own kind until his own head explodes similarly to when Psyker uses his main ability.
Not sure how lore-friendly are such abilities, I hope they are.