This Medela kit converts Lactina kit items to use on the Symphony pump. The protective membranes fit onto the membrane caps. Both dome shaped pieces then fit into the top of the Symphony pump, providing a way to attach the tubes to the pump.
If you have the harder Lactina tubes (#8007213) you can use that on the Symphony if you wish, as it will fit. The only difference between the Symphony tube (#87214 or #8007214) and the Lactina tube is that the Symphony tube is made of silicone which is much more pliable than the plastic Lactina tube.
The breastshields and bottles used with the Symphony and Lactina pumps are the same.