portforward prob on singtel 2700 HG and 323

[playurconsoleslaohor]

hi can i check i am using 2wire 2700 mio modem but it is having problem with my new nas 323. i can ftp inside my network but i cant ftp outside my network unless i enable DMZPLUS mode.

Already tried to port forward using 2wire configuration page but all port dont work unless i use dmzplus then i can connect outside my network

Tried
1077
40000
21
1025
1035

Is DMZPlus mode safe to turn on without HDD being hacked?

I already went through countless reading with no answer

Thanks