i'v managed to solve the issue myself!
i'v just made the belt+10 strenght with okku's essence(i'v used 3 brilliant essences if i remember correctly)out of the frost giant strenght and did work:the result is a huge +10 new frost giant strenght that raised my strenght up to 33 with +11 modifier!!
with a two-handed sword(enhanced only +3 so far) i think i'm on the right way to become a real war machine!
ps
any hints on how to manage the spirit hunger without always worrying to find a spirit to devour every few minutes?