So I think I'm going to go with 6i25+7i78 and pick up a $30 small form factor PC (probably a Dell GX620, which is 12x12x3) with a PCIe slot. The 6i25 the PCIe version of the 5i25. I'm leaning toward that because it is in stock, while 5i25 is "2-3 weeks" in the future. I figure that is the minimum time it will take for them to get them.
I've started looking at the VFD. It's a Lenze E82EV751. (Manuals can be found for the 8200 series, if anyone cares to look.) It's incredibly sophisticated, offering all sorts of analog and digital inputs and outputs, breaking, network configuration, etc. There are pins that should allow me to to conventional analog control, but I'd like to look into more sophisticated features too.
I'd like to figure out what kind of connectors the original uses--they look to be unbranded. They resemble Molex connectors, most of them with 4 pins. All the wires are connected using are screw terminals-very nice. Also, one side of the connectors is rounded around each pin. These are also used for the VFD connections, so they might be fairly standard in Europe. I'd like to find the female connectors so that I can use all the original connectors. If anyone has any clues as to what they are or where I could find them, I'd appreciate your input.