I checked their web site topher, and it looks like the second cable assembly you require, is blue and it's a 15 conductor D-sub serial cable to 8 BNC ends. There doesn't appear to be any audio in the 2nd assembly, it only does audio in the first one.

You had better check the card model number as well, it appears they have cards with only 8 cameras but the pic still shows 2 serial connectors. Hard to say if they are only showing the pic of the 16 unit or maybe the 2nd serial connector is a dummy.

Does the owner still have the boxes to the cards, maybe the jumper assembly is still in it? If not, you might be able to order from the manufacture directly on a credit card. Worst case, a cable could probably be custom made by metering out the first one, not a pleasant job, but doable!