Ok I looked at the ezmarquee manual.
XMT block is for ASCII communication.
What you was trying to do so far, set up slave I/O area and use DPRW_DAT/DPRD_DAT blocks, is for DP slaves - in your case profibus dp protocol.
If your display is not profibus capable these blocks will never work.
So first thing is to decide what protocol are you using and then we can move forward.
I am using profinet.... I am sure it is profibus cable connected to all the ezmarquee and remote I/O