My DD10 doesn't have the official diagnosis from the doc yet, but she most likely has Aspergers, and with that ADD/impulsiveness and Sensory Processing Disorder. She also is brilliant. She's very well read and highly intelligent. She gets concepts well beyond her years, can memorize a song or poem after hearing it once and yet, can't get basic math facts, is socially very immature and basically, much like your son. I could write about her pretty much what you did about your son!
We have rather inconsistently used HOD the last 3 or 4 years. We keep moving or I land on bestest with a difficult pregnancy or whatever...we've just not gotten it done consistently but I can tell you that NOTHING out there works as well as HOD for her. I tried finding things in the midst of the chaotic times to lighten the load and make school smoother, but truth is...it's just not out there. It took some time and some training but now I can see its perfect for her. It's also perfect for my next child, DS7 who is very typical boy except he's a math guru.

I've found placing her in a guide at the oldest end of the age range or in the extension range works best. I found a routine, but not a schedule works wonders. (set order but not set times bc she and I both freak out if we get a couple minutes behind), and having the basics all in one spot to flow from one to the next as quickly and easily as possible (we keep all hers in a backpack by the dining table) and getting those basics done FIRST and leaving independent work for last so she doesn't feel her creativity is stiffled by time limits and I'm
Not bothered by her dawdling and/or extremely detailed notebooking pages. Lol. We also are sure to alternate subjects in a way that makes each a stark difference. A nice change. Math and grammar are different but both are thinking subjects as she says and so we do part of math (which she has come to love recently which is a miracle, but those bar models of Singapore are her visual love.

) then we do something like dictation then finish up math, on to Igniting Your Writing while I do math/grammar with DS7, then grammar with her. This varies often. And I have a block of time for the basics and will often let her choose the order bc her mood has a major influence and the control she has over the subject choices help her control her mood. She couldn't say time for history during the basics block, bc I maintain the real control still. It's basics time

She has no sense of time so a visual timer has been excellent. It's like a huge kitchen timer, but the numbers are on the edge and not on the dual that turns. So she can keep reference of how much time is left with a glance based on where the dial pointer is (kitchen timers have the red arrow always at top and the numbers on the dial that turns making it hard to actually SEE the visual of the amount of time left) Ours also has a red button at the top that starts rising out of the timer the last few minutes and pops up at the end --it says "time's up".
I'm on my phone so it's hard to stay as organized in my typing bc I can't see what I've already written. So forgive rambling and typos! My phone's auto correct can often prove mean or unfit for society so please let me know of any blaring edits needing made, especially any "bad words" it may have chosen. Seriously a rude little techno-contraption sometimes. LOL