You guessed it! I have the CUT OFF FREQ control on my SAWD200 turned all the way up, which is 200Hz. The speaker came with a 20 ft cable with the plug that your are asking about on one end and pigtail leads for the L, R and C channels on the other end. The part number for that cable is 1-823-331-11. Its not available from Sony, but does appear to be available
here for $63.70. The plug is a standard 6 pin Molex connector. I see what appears to be it when I Google "6 pin Molex connector".
For nearly ten years I used a connection from the subwoofer output on my AVD-C70ES to the low level input on the SAWD200. Then, I read why its better to connect to the speaker outputs in the
subwoofer setup tutorial. I installed banana plugs on the ends of the six wires and plug them into the banana plug openings on the AVD-C70ES speaker terminals. It sounds significantly better.