They are tunable in that they can be rebuilt, and you can change the valving by changing the shim stack. You will need Icon's needle fitting to recharge the nitrogen for their shocks, as they don't use a schraeder valve.
As far as I know, Icon only offers 2.5" front coilovers, and besides the large cost difference, you have a pair of spherical bearings on each shock which will wear out often and need replacing. I do mine about every 11 months, as one shits the bed.
The Icon 2.0 rear shocks aren't much different than 5100s. Both 2" monotubes with digressive valving and rubber bushings. If you travel much on gravel roads you will destroy the Icon's in short order without using their "shin guards" as rocks kicked up by the front tires will pit the rear shock shafts and cause the seals to fail.