The second DB25 just give you access to the same signals as the first one, if you want to pass some unused I/Os to some other device. I've never used them on mine. I've used them with the parallel port, both USB and Ethernet SmoothSteppers, and now a KFlop. Never a problem with any of them. I don't recall the shipping cost, but it was quite reasonable, and delivery was always quick. I've also used their spindle control boards - very nice!
You can contact Peter Homann directly at peter@homanndesigns.com.
Regards,
Ray L.