The Extreme range all suck in sand since the're not made for it.
They deform way too much to be usefull in sand.
In sand you need quite stiff knobbies since the ground has to deform, not the tyre (other way around than rocks).
Actually the Mitas C02 Stoneking sucks in the real gnarly rocks but does really well in the sand and even better in mud while also have an extreme long lifetime for a knobby with such high knobs.
If you want to keep that Extreme tyre you could try to air up to 1.5-1.7Bar since the tyre and knobby's will shape better.
Edit: That C02 is my favorite tyre for our offroad season that incluides lots and lots and then a lot more of sand and mud + long stretges of tarmac.
I also really like the Rebel Xplorer 01.
Actually anything with big blocky stiff knobs will do sand combined with road duty pretty well.
In sand a scoop tyre is the best, but hardly any are streetlegal and all suck on anything but sand.
