The main difference on the Icon to the Fox is the internal bump system .
No.
The main difference is one is a bypass and one isn't.
A bypass gives you different effective valving at multiple points in the shock travel.
The icon set up effectively gives you a bottoming cushion, but no different valving where the shock spends most of it's time. You get around this to an extent with a non bypass shock by running a flutter stack on compression, but when you need to move oil quickly, such as on sharp chop, the flutter valving can't open far enough. If you try to tune the flutter stack to open more, it'll blow through the travel too quickly on big hits.
Bottom line is you can tune them for whoop banging, or tune them for sharp chop, but they can't do both at the same time as well as a bypass can.
I found the adjusters to be practically useless, they had to be run on full soft to keep the truck from getting crossed up badly in braking bumps and washboard, couldn't run them stiffer without serious issues in the chop.
Incidentally the bypass shocks all have a similar "internal bump system" when the piston head passes all the bypass bleeds and transitions to straight piston valving.
The icon bypass rears I found to be excellent, I'm no icon hater or fox fan boy, the icon coilovers just didn't perform as well as I'd expected for my terrain.
Like I said, if you're blasting straight off of a well paved road into big g outs and sand whoops, no problem with the icons. It's the square edged, moderate speed stuff you see from well used gravel roads that exposes their one dimensional valving.