I can't seem to find out how does the strobe sync with the camera.
The strobe uses a light sensor located at the bottom of the strobe to sync with the camera's flash - much like using the fibre optical cable, but without the cable.
A quick squiz through the Reefmaster DC200 digital camera and SL960 strobe manual reveals all. The DC200 fires a pre-flash to determine exposure when using the internal flash (TTL). But when using the SL960 as an external strobe you have to select 'external flash' which disables the pre-flash. Which basically means the strobe is not 'pre-flash aware' - it's not capable of duplicating it and neither is it capable of ignoring it (it'll try and do a full dump twice which ofcourse it can't in that span of time).
The strobe only has 3 settings - on/off/test. Which means it can only do a full dump. The manual suggest using diffusers to dial down the output of the strobe for macro. The strobe diffuser is an accessory that can be clipped onto the strobe head in order to modify the brightness by dialing a degree of diffusion.
You also have to position the strobe so the light sensors is to the side or above the camera and that the shine of the cameras built-in flash can trigger the strobe.
Re: the manual flash on the Canon I believe (at least on the S45/S50) you can select 3 levels of flash intensity. So if you select the lowest it should still trigger the strobe and save batteries.
BTW I was quite impressed by the availability of info on the Reefmaster documentation including details like pre-flash interval of 0.2secs.
Conclusion: exactly what I said in my first post - manual (full dump) and you'll have to use a combination of f-stop, distance (which is limited since you have to keep the strobe close to the camera) and diffusers to control your exposure.