Matthew,
You might consider an M Series PCI Device. Those boards will interface well with the SCB-68. However, you will need a different cable. Take a look at this site:
M Series Multifunction DAQ -- the Next Generation
http://sine.ni.com/nips/cds/view/p/lang/en/nid/14114
As for USB devices, there aren't any that will interface well with the SCB-68, however, most have built-in terminals (Like the DAQPad 6015/6016. Check out this site:
USB Data Acquisition
http://www.ni.com/dataacquisition/usb/
-Alan A.