Can the FTG end of a propress fitting like a FTG X C have a propress fitting pressed on it?
The Q & A below at Rigid afirms that you can solder a FTG end to a copper fitting, but does not state whether a FTG end can have a propress fitting pressed on it.
Q - Are there ProPress fittings that can be crimped on one side and soldered on the other?
A - Yes. For example, a user can solder the FTG end of a 90° FTG x C elbow and crimp the other end. When doing so, a user must first remove the EPDM seal, solder the other end and replace the seal once the fitting has cooled.