I was referring to a parallel cable between the parallel port board I added to the Pi and the camera. Sorry if I wasn't clear - I gave up trying to find a USB to parallel converter that works with the Linux kernel "parport" driver stack. That is what "sbiglpt" (SBIG parallel port Linux kernel driver) wants..
Even if we could find a USB converter, I think it's likely not to work. The sbiglpt "bit bangs" its protocol, polls bits on the parallel port in busy-loops, etc.. If access to those bits becomes a USB hop away, there may be issues meeting the camera's timing, busy-waiting too long in the kernel (or timing out), etc..
There are all manner of fun projects possible here though, such as replacing the raspberry pi in my solution with a microprocessor that speaks SBIG's USB or ethernet protocol on one side, and the camera parallel port protocol on the other. However that involves some reverse engineering of the USB/ethernet protocol and so would be pretty labor intensive. I went with the Pi because it allows the old sbiglpt driver to be reused with minimal effort, and the Pi can serve as an adapter that provides an INDI camera device.
p.s. thanks for the CCD info. I actually bought some class 3 KAF-1600 chips on ebay and took my camera apart. There's a fixed program 8052 clone in there (Philips SB7C752-1N28), a PLD, and a Lattice ispLSI 1016 CPLD. Looks like only the CPLD is programmable so I wonder if chips have to be replaced to upgrade the CCD, or if maybe it's just a matter of updating some EEPROM in the CPLD?
The answer to the question of replacing ICs within the SBIG camera is definitely, no. I never had to replace or rewire any circuitry going from KAF400 to KAF1600. Its only a software and rules thing.
As for the interface to usb, I must search again, but when I built my Audine camera, there was a usb interface which a guy made called the Quick Audine. It used a factory made FTDI based usb interface coupled with a PIC18F252. At the time when I built them, I did not think it was too difficult. Such an interface might give you some ideas, but, as you say, it is a singular hardware solution.
On chip upgrade: Ah that is good to know! I did just find "Application Note: Using the Advanced Menu to set the Camera Configuration" with a google search. Apparently CCDOps has an "/advanced" command line option which causes a new "advanced" menu to appear. This menu has a "camera configuration" command which can update the camera EEPROM (camera type, anti-blooming flag, tracking chip type, power-on cooling mode). Maybe the camera type could simply be changed from ST-7 to ST-8. Does that sound familiar?
Audine: so cool! So you built one huh? But trying to stay on topic, I agree a thing like the pic+FTDI (or modern equivalent) would be perfect here. The missing piece is IMHO the SBIG USB/ethernet message format/protocol, so this device could plug right in to SBIGUDRV and all the software built to use it. (I did ask DL if they might consider releasing the network protocol specification a few months ago and they politely declined).
Answer to the question on just changing from ST7 to ST8, yes. But there actually was a file which does this flash. I know I have it some place, but wow, its going to take some hunting to find it. Sounds like you might have the answer with the CCDops program.
Sorry to read about the decline to release the old code, its a shame since SBIG was literally the first camera I can remember which supported Linux. And you are definitely on the approach which I am looking at. I thought the code in the link might get us there, but if not, I will dig a bit more.