I have been following your progress with interest on the various forums.
I have a working c5 except the cassette, I first thought I cannot be bothered moving
the lathe to sort out after I tried previously alternative interface board and cassette unit.
Then I was making a batch of 50 identical parts cycle time 8.1/2 minutes involving a few stops for coffee food etc. making these I though it actually would be nice to save the running program instead of bringing the computer out to the workshop each time.
So being as I only wanted to save the running program I looked round for a storage
unit to save it as serial data from the rs232 port via g66.
I came up with a universal serial buffer W&T 88642 4mb storage off ebay (quite expensive new) this works ok to upload and download from the c5 or MFI
Im sure other units may be similar, although it can only save 1 program this is ok as it can be left next to the lathe during stops.