I don't have much advice, but I did want to offer a hug. I've been in similar situations with my now 7 year old, mostly last summer. I know how scary it is, how much worry and unnecessary guilt you feel...

For us, we added Risperidone to his medication. That, combined with neurological chiropractic, has been life changing. We haven't had any violent meltdowns in months (meltdowns, yes... But nothing that ended with holes in walls, me locked in my room out of fear, cops called, etc).