Here's the way I do it. To get the strands out of the sheath in the first place, I cut off the end (actually, you'll need to cut both ends, if they're melted) to get rid of the burned part that keeps it from unravelling. Then I grab the end of the strands and yank a few inches out. I then pulll the sheath back, off the strands. When the sheath starts to "bunch up", keep hold of the strands and use your other hand to smooth the bunched up sheath towards the far end. This eliminates friction on the strands, and allows you to pull more free. When you bunch up the sheath, pull it tight again and repeat as many times as it tiakes to get the whole thing seperated. I can usually get 5 or 6 inches of strand out before needing to work the sheath down.
Once the strands are out of the sheath, the easiest way too seperate them from each other is to untwist them, one at a time. Holding the strands in one hand, use the other to spin them the opposite way they're wound together. Then put a finger from the hand holding the strands under a single strand to keep it from warpping itself back up. Work that single strand down until you reach the point where you stopped unravel;ing, and start the process over again.
No doubt that this is stilll a tedious exercise, but it's the best method I've found for unravelling long strands of cordage. Obviously, shorter hanks will be eaiser, but then you have to tie hem all together to make a usable length, so it's worth the extra hassle to do it the harder way.
