Chaps,
The phamtom mode in 430 creates a centre rear sound from (rear Rt and Rear LT) without using an actual centre rear speaker. When you use an actual speaker (6.1 set-up) this is known as discreet. Any 5.1 discs or 6.1 can be used to produce phamtom 6.1. The idea behind it is that you can experience 6.1 sound without the need for that 6th speaker (like in small rooms, or room not feasible for that extra speaker). It is a very good comparmise.