I've got Koni DA on both ends of my Gen 1 Rx-7. Truly wonderful, but it took me the better part of two seasons to figure out the tuning... You didn't say if your fronts are rebound only, or hybrid compression and rebound adjustment. You said they are Koni, so I suspect rebound only.
Here is the simplest advice I can give:
Use compression damping to get the car to handle over bumps and kerbs. Axle hop = too much compression damping.
Use rebound damping to adjust corner entry and exit understeer/oversteer balance.
More rear rebound = more oversteer.
Less front rebound = more oversteer.
Less rear rebound = more understeer.
More front rebound = more understeer.
Remember that dampers only work when the car is in TRANSITION. If you car doesn't handle correctly in the middle of the corner, dampers will not fix that.
What I can not explain, is how to recognize that you have too much rebound damping at BOTH ends. The balance is right, but the car is not as fast as it could be...

Good luck!

Tak
#29 ITA
SFR SCCA
[/b]
Generally true. Too much rebound usually manifests itself as the car "jacking down" (which of course without shock pots connected to your DAS you won't be able to tell unless you start scraping the oil pan for no apparent reason) or overall loss of grip, which again you might need to look at your DAS to see.

Before I go into details, what exactly do these shocks adjust? High spped bump, low speed bump, high speed rebound, low speed rebound, and are they digressive valving or other? My guess is the high speed stuff is set by the valve stack and all you have is low speed adjustments. Confirm and we'll take it further.