Fleck, Clack, Autotrol all make different heads for different applications and marketing purposes.
The 5600 will not work with Filox or Pyrolox. It can only handle approximately 7 GPM backash rate.
If you have a 7000, it can easily handle Pyolox but do you have enough water to properly backwash it? Pyrolox and filox are typically backwashed at 12 GPM on a 10" diameter tank for 5 minutes every few days.
If you have a cistern, you may have some better options. What size pump do you have feeding the house? How many GPM? Can you install the water treatment after the cistern?
And, it is Fleck, not Flex. From the name Fleckenstein. Here is a nice article on Andy Fleckenstein. http://www.jsonline.com/news/milwaukee/49559287.html