Just in case anyone's interested, I've just stuck a Black Box rebound damper assembly in a Sektor Coil U-Turn fork - the original Sektor damper does, as people have told me, include a negative spring which sits kebab-style on the damper rod. It's a pretty feeble spring, to be honest and I wonder how much it actually achieves, maybe a little car park plush on the initial spring movement.
Anyway, after some thought, I popped it back onto the Black Box damper rod on the basis that it fitted okay and I can always take it off if things feel wrong, and screwed it all back together.
Haven't ridden it yet, so I have no idea what it'll do the fork in real life, but all being well, it should basically upgrade the high speed rebound so it copes better with repeated high speed hits - flat out through rockeries etc, which is where non Dual Flow RS forks tend to choke and kick around.
Will hopefully get out on the Pace tomorrow somewhere rocky and fast and will report back. If it works, then it's a 70-quid upgrade to a fork that only cost me around £300 that should give it a bit more high speed control and make for a very nice trail fork.
I also have a spare Pike MoCo which I might bang on for the added flood gate adjustability, but I'm not sure it'll make any real performance difference.
Just in case anyone's wondering, the rebound damper transplant is a dead easy, 15-minute max job. Basically pop the lowers off, undo circlip with fork legs inverted to stop damper oil pissing out, slide out rebound damper assembly, lube o-rings on new damper assembly, slide back in carefully, reinstall circlip making sure it's fully seated, pop legs back on and add some lubricant to compensate for any you've lost in the process. Job's a good un.