Try
roll[dice_]:=Module[{attack=Sort[Take[dice,3]],defend=Sort[Drop[dice,3]]},
If[attack[[3]]>defend[[2]],{0,-1},{-1,0}]+
If[attack[[2]]>defend[[1]],{0,-1},{-1,0}]];
Map[{First[#],Length[#]/6^5}&,Split[Sort[Map[roll,Tuples[Range[6],5]]]]]
which in a second returns exactly these probabilities
{{{-2,0},2275/7776},{{-1,-1},2611/7776]},{{0,-2},1445/3888]}}