For those who are interested, I found a source for a serial cable that connects the SL-5500 and a female db9 connector (like the cable that comes with Garmin GPS Units).
You want to go here:
http://www.serialio.com/products/ada...ZThinCable.htm
and ask for or look for a:
M-DB9-4 cable. 4 foot cable or
M-DB9-6 cable, 6 foot cable.
They only have 30 or 40 of them left and they don't intend to make any more.
I got the 4 footer and it came to $40 including shipping