Well, I've always personally contended that the dust covers veil the detail on the HD800. My own statements in that regard have fallen on deaf ears... rather no comment. I've been running stock with the Crack amp for a couple years and finally broke down and put together a mainline which was a huge improvement. I'd forgotten about removing the dust covers until now. The mainline is a real detail oriented amp but still very smooth and polite with the HD800. The mainline has potential to run nicely with the dust covers removed, but a better replacement is still required. So here I am.
I didn't find the thicker rug liner locally yet, but I did find thinner shelf liner at Wal-mart. 'Duck' branded 'Select grip' easy liner. I've also found double sided tape to adhere to the shelf liner a bit too much and if you need to replace then you're possibly cutting out new liner. I've since tried out Scotch reusable tabs. Seems to adhere to the liner and cups in place enough so far and there is no fight at all removing it. Apparently the Scotch reusable adhesive can be washed if it accumulates too much oil and starts to loose its grip.
The shape cut is a bit of a challenge. After refitting just liner and the trapezoid piece craptology foam I think its the best mix, but I'm convinced the easy liner that I'm currently using is not quite dampening the shells quite enough compared to the original dust covers. So what I hear currently is a ton of space and detail and the trapezoid is doing thing. Its all a bit on the hot side. A lot of my inner metal ring that holds the driver in place is exposed. I believe that is also contributing to the hard effect I'm still hearing. With the craptology ring it was over-damped.
I'm thinking to use the current ring pattern to cut a layer of shelf(rug when I find it) liner to get that covered properly since exposed it definitely adds to the 'hard' nature of when you have the headphone running without the dust cover. I'm planning to that cut ring and bond it to the my existing liner using double sided tape for a permanent bond. I hope the result will be a dust cover shaped section of liner that fits in like the original. I'll report back how that works when I have time to get to it.
Definitely have to find the rug liner. The easy grip shelf liner better than no dust cover, but its not cutting it.