I'll take a stab at helping. In order to use the 584 board and the DL-900 software, the basic Caddx system has to be running and configured to at least talk to each module and have serial and other items working. It's like connecting to a PC - you have to have the basic PC running in order to connect to it.
Therefore, you have to have the 584 board programmed intot he Caddx NX-8 system via the keypad first.
Also, the DL-900 and Caddx basic default user is "caddx" with a password of "1234". When the DL-900 starts up, it will ask for this info twice. If you have changed the defaults in the NX-8, use your values.
Luckily, a new post on the HS board outlines the basic panel configs in preparation for Nitrox's plugin, and this is exactly what you need to get the Caddx board working even for the DL-900 software. See
http://board.homeseer.com/showthread.php?t=99873 .
You also may have a problem with the serial cable. You want a straight-through cable - not a "null modem" cable - for the 584 to PC connection.
Once you check that all out, post here or email me and we'll see what the next steps are based on where your problems are.
Hope this helps!