Desperate for Advice on New Cat vs. Old Cat

I rescued a male tabby cat and he lives in my home with my two resident
females. I did everything by the book as to how to introduce them. Kept
him in the room for weeks, slow introductions. When they finally did meet
the male violently attacked my older female. Weeks later he attacked my
younger female. Weeks went by again when they were seperated and I put
him into our master bedroom, not knowing my younger female was in there.
Well he found her and attacked her, I broke it up, she ran, he chased her
and attacked. This went on several times. She would run and he was
relentless attacking her. I'm at witts end with the male cat. He is
seperated and lives upstairs rotating thru the bedrooms. My females run
and hide if they hear him meow or even the jingle of his collar.

I'm very distressed as I've grown attatched over the months to the male
cat. However, I can't allow my resident cats to live in fear and get beat
up on.

I've tried cages, petting him while petting a resident cat in the same
room, rubbing the cats' scents on towels, etc, feliway--you name it.
REgardless, he tries to attack them every time.

All cats are neutered. It's been 5 months that this been going on. I
feel really guilty making the male cat live in the bedrooms but don't seem
to have a choice.

Any suggestions? Anyone with a similiar situation that ended happily? I'm
considering drugs for the male cat or a cat behavioralist--any comments on
these? Any advice you can give would be so appreciated--you have no clue
how this situation worries me.