Out of curiosity, would it be imbalancing to have the 'negative levels' bestowed by Psychic Drain increase by one per 5 HD after your first (2 at 6HD, 3 at 11, 4 at 16)? Or maybe 6HD (2 at 7, 3 at 13, 4 at 19)?
I only as because, at higher levels of play, it doesn't seem like you'd have much chance to actually use this class, because it would be too hard to incapacitate anything worthwhile. Having the 'negative levels' bestowed increased would really help with that. Otherwise you are locked into using "Save-or-Lose" or "No-save, Just-Lose" rocket-tag tactics just to get to incapacitate and absorb things. It seems like making the class so that it is less reliant on those tactics means that it can just maintain to use its debuff that combo's into its other abilities even in late-game.