I have a 6 feet tank of Malawi cichlids too, but i dont think it is adviseable to put in drift wood. Because drift wood tense to make the water PH unbalance and the acid level will be higher.

If you are going for Malawi cichlid i suggest that you put broken corals and fine sand at the bottom. Then some huge corals or maybe some life stones or dead one also can. (dead stone are those corals plate that died and normally its white in color).

Add some salt to the water because Malawi lake where the chiclids are from connects to the sea so there will be a mixture of salt and fresh water. Then only it will brings out its color. They are very hardy fish so wont give any problem just that they need a big space and plenty of tiny caves or place to hide.

Most chiclids are teritorial and they will fight until death. Therefore u need to prepare plenty of hidding place for them.