It's gotta be the cable. As Rick said, it has to be a specialty serial cable that inverts the send and receive pins on one end.
People have used Apple Imagewriter data cables in the past, as they have the proper reversed wiring. If you try to use a standard DB9 serial cable instead of an Imagewriter cable, it won't work. You'll need to reverse the send/receive pins on one end.
An easy way to do this is to use a "null modem" adapter, available at any electronics supplier or Radio Shack. It is a small plug adapter that reverses the required pins and allows you to connect your DA7 to any Mac or PC's RS232 serial port.
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Audiophile: "A gate IS a compressor, A Fader is a MANUAL compressor." Pure comedy.