Either try the firm spring with more rebound damping and the floodgate out. Bearing in mind the rebound adjuster theoretically only adjusts the beginning stroke rebound, it could be that the factory tuned end stroke rebound is to fast for you with your firm spring in it. In that case you'd have to find out how to tune it yourself or send it to loco/tftuned.
Or go back to the medium spring, keep the rebound quite high to keep it up in it's travel, remove the flood gate and run a bit more low and high speed compression (you already have to add more just to get to the same amount of compression when you remove the floodgate, so add a few more clicks and then some more).
So it's either that you are running to fast a rebound with the firm spring, or simply you are running to firm a spring. Also a bit of brakes dive is useful, it allows you to brake before a tight corner, moving your COG forward and shortening the wheelbase which makes it easier to get round the corner. Brake dive is one of those things weekend warriors try out in the car park and then proclaim "it's to divey"...it's not that big of a deal and it can be tuned out...but lots of people are obsessed by it and end up tuning it out or running such a stiff spring rate to the point that other areas of the forks performance is compromised. The real problem is when forks blow through their travel over terrain.
As always until we have computer controlled suspension with brilliant artificial intelligence that can tell what you need in terms of spring rate and damping at the correct time then suspension tuning will always be a trade off.
The other alternative is to get an Avalanche damper and start playing around with midvalve tunes.