My cash is limited and had been looking at lower end Yamaha's in the 200-$400 range. Been told to saty away from low end yamaha's. What do you think of the denon DHT-684DVD or AVR-683. Or should I just pony up and get the AVR-1604 or AVR-1804. Also if I were to by say the 1804 which is 6.1.. could I run only 5.1 speakers. Can the rear center be turnind off?