Ignoring him might well help- but not making him feel that you are comparing him to the other children! It's the sort of thing that sometimes slips out, but really it's something we should avoid at all cost. It only increases resentment.
This is clearly very tiresome behaviour, but I don't think it is abnormal or OTT in a 6-year-old boy. IMO it sounds less worrying than when my ds started hurting himself after a bereavement last year, though the reason is clearly similar. The things I did then was: acknowledge his pain, explain that he had to learn to take it out on something safe (showed him how to beat up the bedding), and give him a special password he could use if he needed me to take him to one side so he could talk about the bad things that had happened.
My dd had spectacular tantrums when her disability first became apparent (age 7/8); in fact, I've still got the scar where she bit into my hand. She got herself into the sort of state where she really didn't seem to recognise the people around her. As she is a tall well built girl, it did require quite a bit of handling- mainly by me as dp is a bit of a whimp about these things. I used to restrain her gently but firmly (from behind, arms pinning down her arms, and one leg up around her legs) and just calmly repeat: 'no I can't let you hurt me/little brother'. I felt that she needed more than anything to feel that there was somebody there who was strong and powerful enough to control her without getting frightened, at a time when her feelings were too strong for herself to control. I also spent lots of time on activities together, and treated her in a more grownup way when she was being calm.
Your ds's tantrums don't sound as bad as this, but I think the principle is the same. What they need is the safety of feeling that there is somebody there who can handle the situation and who is not frightened or at their wits end- and who will never love them any the less. Someone who has the strength to go on indefinitely protecting them from doing something really bad. All right, so you won't actually feel this- this is the bit you have to fake! Practise in front of the mirror.