Try this one and copy it on your item_db.txt (replace the original one!)
5592,Sigrun's_Wings,Sigrun's Wings,5,20,,100,,2,,0,0xFFFFFFFF,7,2,512,,80,0,568,{ bonus bAgi,6; bonus bDex,6; bonus bVit,6; bonus2 bAddRace,RC_DemiHuman,1; bonus2 bAddEle,6,5; bonus2 bMagicAddEle,6,5; bonus2 bSubEle,1,5; bonus2 bSubEle,7,5; bonus2 bSubEle,2,5; bonus2 bSubEle,5,5; bonus bMaxSP,100; if(getrefine()>=16 && getrefine()<=20) { bonus bAgi,2; bonus bDex,2; bonus bVit,2; bonus bMatkRate,3; }},{},{}
That code works for me.