I had this same challenge when I first got my X. If you can access the memory of the EnV via USB, then you could just drag/drop the ring tones from the EnV ringtone file to your computer, then drag/drop them into the Media>ringtone file on your X's SD card (via USB connection).
If you can't access the EnV's storage, then I suggest you google EnV ringtones and see if someone has done the work for you. You can then download them to your computer and, as above, drag/drop these files to your X via USB (the option for the connection will show in the notification panel once the USB is plugged in).
Note: Do not install or use the Moto program that wants to be installed when you connect the X with your computer. You don't need it (not sure what value it has at all). Just click cancel... every time. PITA, but worth it.