CPS-2 optical interface???

Long ago I heard this rumor that Eco Fighters could be played with a spinner that would replace the buttons for clockwise and counterclockwise gun rotation, thus making for a gameplay identical to Forgotten Worlds'. Since I could not see how an optical device could be interfaced with the CPS2 hardware I always thought it was BS (the US manual of the game doesn't mention anything in this respect). But recently I found some clues that seem to back up the possibility that CPS2 makes use of optical controls.

The Japanese flyer of Puzz Loop 2 clearly shows that you can choose either a stick or a spinner. Take a look:

http://www.arcadeflyers.com/?page=flyerdb&subpage=flyer&id=2070&image=1

However, I still couldn't see how it would be possible to interface a spinner with the CPS2 mobo, since you need special hardware to encode the optical signals of the spinner. The only thing I could think of was an interface like that of The Irritating Maze:

http://www.hardmvs.com/images/IMaze/IMtbBoardInstalledRSM.jpg

But with no evidence for such an interface this was mere speculation. Until I came across an ebay auction for a Puzz Loop 2 board. Take a look at the auction picture:

http://www.boomspeed.com/nassivera/PuzzLoop2.jpg
(the spinner option can also be seen on the instruction sheet in the pic)

What else can that small board be other than an optical interface? It's very similar to the IM one: Jamma male connector, a smaller connector for the spinner and it should also have a female Jamma connector that plugs onto the mobo although this can't be seen from this pic.
Unfortunately I didn't win the auction so I don't have definite proof of what I'm saying.

Anyone have any inputs on this? It would be cool if the optical interface actually existed and could be used with Eco Fighters as well...

13 year bump! Did anyone figure this out?

I wonder if the JAMMA edge reads quadrature encoder sensor outputs on two button/stick inputs.