apart from TCP 5555 from Cell Server to DMZ Client, you need as you already might know, data ports from DMZ to Media Agent AND crs / xMA Port from DMZ Server to Cell server. crs and xsm are required aditional for integration backup. those two port ranges are not required for file backup
what entries do you have in your omnirc file on the cell server under "OB2PORTRANGESPEC"?
if you have xMA-NET:<range> then you also have to add CRS and xSM. So it could look like this