Damping is generally tuned and matched to spring rate at that corner, then fine tuned with the rest of the car. While it may seem that wow - a coilover has 16 positions - the reality is that there's only a limited set of positions that are optimal. In the rears, since you're running OEM coils, you're finding that you need less damping to match with the softer spring rates. Conversely, at the fronts with higher spring rate coils, you need more damping.
Part of the trouble with many coilovers and their abundant settings is that the end user has to dial it in. Sure, it's not lost on me that it allows for flexibility. At the same time, dialing in suspension is something OEM and professionals take seriously with lots of tuning time in various conditions. Sometimes it's almost better to have a tailored and tuned setup straight from a reputable manufacture. Higher end stuff will include a guide with suggested calibration which is the only stuff I'll consider. If I pay for high end coilovers, you betcha I would expect them to do the leg work to give me a optimal calibration that's been vouched for and tested. I'm paying for the tuning.
In regards to re-valving just the rears. Just my opinion but I believe you may be running in circles getting this dialed in. Suspension setups are a tuned set. Mixing and matching front and rears will make for an unbalanced handling setup, especially with such disparate spring rates. Just another idea would potentially be to run OE coils the front too (if possible). And use the adjustable damping of the Icons to get the ride you want? It might work rather well with the digressive shocks for more body control without the harshness of stiffer springs.
