DS's aggressive behavior seems to be very successfully triggering rejection behaviors in your DH. Because he doesn't realize that's what is happening the cycle of aggression and rejection continues. Your DS may have been wired this way by his very early experiences. I am not an expert but if his behavior is related to attachment and security then Your DH needs help to be able to confidently reinforce that he is not going to go anywhere, reject your DS or abandon him and find some strategies to help him do this.
Children with ADHD also 'cue' and filter cues differently to those without ADHD. If we get the 'cues' a bit wrong (which we frequently do!) it can also trigger unwanted behaviour. As kids with ADHD get older, many learn to manage the 'off-cueing' and get better a filtering the stimuli around them. in the meantime, DC will be experiencing life on a different wavelength and will be, by the end of a day, like a coiled up spring of frustration. Who is going to get the rough end of that?? Mum and Dad!
It is interesting that his aggressive behavior was triggered by the taking away of the computer game. Children with ADHD are particularly taken by gaming because of the level of stimuli they offer. Children can easily 'over focus' on them (and become addicted in some cases), therefore drowning out the white noise and frustrating levels of feedback they get from the environment around them. To have his focus suddenly moved will have meant a massive and jarring shift of focus for him. and boom, he reacts!
It sounds like you are doing a really brilliant job but things are a bit tougher for DH?
He is still a fairly little boy OP. If he was 11 or 12 i'd be a bit more concerned.
Do go back to psychology and ask for a Child and Adolescent Mental Health Service Referral and ask them to do some work with you and DH on managing aggression and building attachment. He is only 7 and from what you say about his behavior with other children and family members things are otherwise pretty good. Are you and DH getting enough time as a couple (who does when they have kids?!) That might help.
If I was working with you, I would have a pile of suggestions for your DH, trying 1 or 2 new things at a time.
It sounds like you are doing really well with your little boy and as he goes through new stages of development so the new challenges will arise.
All the best to you.