Eatriskier I know I'm coming to this a bit late, but anyway...
I'm not your husband (honest) - but I could well have been a few years ago.
Fortunately my fantastic wife was dogged, determined and infinitely patient and we got to a solution where I've got it under control - which is impressive given that I come from a long line of clutter obsessives - I can't think of any house of any of my blood relatives that wasn't full of clutter.
90% of the comments on this thread are completely useless, but fortunately you seem to have the insight to recognise that it is a mental condition that you are dealing with and it's certainly a condition that can be addressed.
I could go on all night about this, but I'll just cut straight to our plan, which fortunately seems to be broadly similar to what you're doing, but there are a couple of points to note.
(actually I should probably say it was my wife's plan, tbh)
It's important to not try to battle on too many fronts at once.
Firstly, pick one room - the living room is the obvious candidate.
Sit down with your DH and agree on a design for the living room. This includes -
- What furniture is in there and how it is arranged
- What shelving etc there is and what is stored on them
- What books/DVDs (e.g. max 20 books, max 10 DVDs + 20 for kids)
- What pictures on the walls
- Decoration etc
- Agreement on a 'system' for kids toys etc
Basically, as much detail as possible about exactly how the living room is supposed to be and how it is supposed to function.
Then get your DH to document the design using whatever technique he wants (e.g. as a drawing, a written document, a list - whatever).
The important bit is to get him to 'own' the design.
Then agree with him a realistic timescale to implement the design. It then becomes his project - something new to concentrate on/control/obsess about.
The subtle difference here is that, instead of you saying "I want you to get rid of this, get rid of that..." you're saying "here's a clear objective of a room that I'd like you to create for us". It's a creative process, not a destructive one.
Diverting obsessive behaviour towards creating a positive outcome is more likely to succeed than battling, canute-like, against negative behaviour.
If you succeed with the living room, then you move on to the hall - you said you've already got the kitchen under control so then you've got the ground floor ready to receive visitors. And then on up the stairs...
Of course, it might not work - your DH's obsessiveness might be different to mine - it's a complex spectrum, not black and white.
But it worked for me - I'm not completely fixed yet, but i'm getting there, bit by bit. I now obsess about keeping the living room just as it's supposed to be (along with lots of other things).
The key thing is that you've got to get your DH's head in the right place. For each category of stuff you've got to implement a new rational thought process (I call these 'systems') which supercedes the default system of "keep everything". Otherwise, when you take away the stuff, you just leave a big mental hole that needs to be filled - ideally with replacement systems that make the stuff unnecessary. I worry slightly that your only focus is on making the stuff go away, and not on making it unnecessary.
Anyway - If your DH doesn't beat you, doesn't abuse the DCs, isn't an alcoholic or drug addict, isn't a gambler, doesn't cheat on you with other women (or men) then I would tactfully suggest that he's worth persevering with until you've at least tried some things that might actually work.