Hi, They are the same aside from Storage Server 2016. 
is an NX3230 just an 730XD with Storage Server 2016 Pre installed? Reason for asking is that im looking to replace an old Dell NAS and on the pricing i have received the NX is more expensive but does not appear to offer much over the 730xd apart from having storage server installed (which has the same features as standard from a storage point of view).  
NX3230 or 730XD thoughts