...says that using an extractor to help dry your bag can lead to clumps. The Centrifugal force an extractor applies to your bag, while effective at removing water quickly, works to compress the down inside each baffle into the smallest possible cross-sectional area given the speed of rotation and distance from the center of the drum. Thus, the "best" extractors are also the most effective at compressing the down.
Looking at my bottle of Nikwax down wash, their recommendation is to spin the bag in a front-loading washer 3 times on the slowest setting possible. There is no mention of using an extractor; perhaps this exclusion is not accidental?
I washed/dried my REI Kilo Flash using an extractor the first time, and it ended up re-clumping quite quickly considering it's seen only around 30-50 nights use since then. I am currently washing the bag again as I type this, and will dry it this time per the Nikwax suggestions, without using an extractor. I'll try to keep all other factors constant, and report back when I've again racked up another 50 nights in the bag.
Until then, I've given up on extractors...