right, so the idea behind those DE assassmo's are;
- ASF + I10 = re-rolls to-hit.
- lots of attacks to overpower characters
- KB to ensure the offending characters die horribly!
- scouting, skirmisher w/rending stars + manbane for annoyance value.
so, to combat that with your warriors, here's a few ideas;
- give your fighting characters the mark of tzeentch + ward save. throw on one of your 'immune to KB' suits for your lord/s and you have one helluva tough nut to crack!
bronze armour + talisman of protection even leaves room for a killy weapon...
- if you take exalted champs, don't put magic items on 'em! against elves, they don't need help beyond a MoT + extra hand weapon or even sword & board... T3 vs chaos means things go squish pretty easily...
- take a hellcannon and obliterate the unit.
- don't send characters into the combat!!! seriously, elves drop like flies to hard-core fighty armies like chaos... a unit of Tzeentch warriors or chosen w/hand weapon & shield will fight those assassins all day long.
remember too that assassmo's are still characters, thus you can simply allocate rank & file attacks to them.
- magic the unit. the slaanesh spell ecstatic seizures is particularly nasty towards elves.
treason of tzeentch will decimate any dark elf unit! or you could just try for the gateway approch.
not taking a mark of chaos allows a sorc lord to get heavens magic. curse of the midnight wind is a particularly funny way of dealing with assassins since it all but negates their KB postential! iceshard blizzard also helps take care of a missile unit too, or even the offending assassin's unit.
anways, hope this helps,