Multi boxing melee classes would be hard but i'm sure it can be done.. Here are the specs i would go with the melee classes:

Deathknight - Unholy, the pets can stun the target and if you keybind the stun and set it on round robbin you could probably stunlock a target just with the pets, you could also kill multiple targets by putting the pets on one target and killing the other target with your guys. Also could set deathgrip on round robbin to pull back casters, deathknights are probably the best melee classes to box :O

Warrior - MS spec, 2x MS = 0% healing xD

Druid - Feral, It might be good just to stack bleed effects lol :O

Rogue - I would go mutilate and set stuns as round robbin

Overall, multi boxing mele classes is good in theory