Hi
I would be surprised if the AF35 is not physically compatible with your SD800IS / WP-DC9 combination. The AF35’s tray should come with appropriate hardware to enable you to mount your WP-DC9 on it using the tripod screw on the bottom of the housing.
The AF35 is designed to be about as user friendly as it is possible to be for an underwater strobe unit. There is a sensor that points towards the flash on your camera, and enables the strobe to replicate the flash duration used by your camera, so its is essentially fully automatic. If you camera flash fires, the strobe will fire.
There is a control dial on the side of the sensor that you use to select the power level of the strobe. It appears that you can set this by trial and error - i.e. picture too dark, increase the power level, picture too bright, decrease the power level. Apparently, once set, you can leave the control alone.
You will not need a fibre optic cord (or any other accessories) - the AF35 is an all inclusive kit. You may however find better results are obtained if you block the camera’s flash by taping over the housing’s diffuser, or putting an opaque card in the diffuser somehow. This stops your camera’s flash light going forward to the subject, and bouncing back to the camera, thus eliminating a primary cause of backscatter. Because the AF35’s sensor is off to the side of the camera flash, it detects the camera flash because of the ‘splash’ of light that comes out sideways rather than forwards.
Hope that helps
