A hub should not be necessary for the setup you described.
Additional steps may be needed to make the interface work. The DRS25A was first available in 2008. With original system being a NN3D that used a DHCP process to assign IP addresses to peripherals. After the NN3D we went to the TZT1, TZT2 and now TZT3 platform that does not use a DHCP process.
This is a long way of saying, depending on the age of your DRS25A, it may need a software update to be fully compatible. The software needs to be at least version 1.16.
The DRS25A also required the PSU-013, additionally you will need to insure that a jumper on J7 is applied, this will bypass the power sync signal.