BNF is a Spektrum brand acronym that stands for Bind N Fly. Binding is connecting a receiver to your transmitter. You can bind your DX5e to practically any Spektrum receiver except the now obsolete AR6000. Of course there is little point in using receivers with more channels than your Tx.
So, no, you are not limited to only BNF aircraft. You fly anything with a Spektrum receiver that can be flown with five channels or less.