Ok I found  KEYSPAN USB CARD software CD ver 1.1 that lists it works on 8.1, it doesn't say 8.0, just 8.1.  

It says it uses apples driver in it so at least 8.1 had USB support from apple and extended to PCI by 3rd party.  So I will try the driver on my 6400 in 7.6 and see how it goes. 

The document with it says something about serial to USB for legacy machines.