Hi Alan fx helmet' are acceptable for 501st membership but they are deemed too un-accurate for the next level which is EIB status.
If you are looking to upgrade your lid to something more accurate there are plenty to choose from. AP, TE, TE2, TM, ATA, RT, GINO, DL the list goes on and on..
I would take your time and have a good read here i think there will be a thread to give the low down on all the helmets i just mentioned here, another good place is starwarshelmets.com
Research, research and more research before you buy