With my Ikelite housing the PS-S80 I reused my old analog Ikelite Substrobe 50’s and SS300 @ 1/4 power. I bought a Heinrichs Weikamp’s Digital Adapter (around $135USD) and mounted it with bungee cord just above the internal flash area using the Ikelite Flash blocker (or make your own using a piece of solid plastic).
The Digital adapter is configurable to handle the preflash or manual but if you need to change it you’ll have to use the magnet that came with the adapter while on land or underwater. One note of caution: Since I was using the old Ikelite strobes, the ss50’s did NOT have enough capacity to keep flashing the strobe to tell me how the configuration was going so I had to use the SS300 at 1/4 power to be able to get thru the whole configuration. I don’t usually make this kind of change to my Digital Adapter once I get underwater or away from home. Set it and use it that way.
Able to reuse my Ikelite sync cords (Nikonos) 5 pins to the Digital Adapter. They also have the Sea&Sea;version.
I shoot the PS-S80 in MANUAL exposure mode, flash output lowered to save battery, internal flash always on in order to trigger the Digital Adapter to fire your analog strobe. Even though the PS-S80 is in manual exposure mode, the Digital Adapter can provide a TTL function to squelch the strobe when there’s been enough light reflected back to the Digital Adapter. You can turn this off if you don’t like it, but for me it has worked well.
Using 2600 Ni-Mah batteries on the SS-50’s and the Digital Adapter with TTL I manage to get 200-270 flashes before needing a set of 4 batteries changed.
One tip I have to offer: Shoot the camera on land with everything assembled for underwater usage. Learn how it works or not. Move the digital adapter to where you get the best images. Figure out how far your strobes need to be away from the subject. Try out the other config settings if you understand what they do. If not, then take the standard default for shooting your Powershot in Auto/programmed/Shutter/Aperture mode
meaning the preflash will be skipped and your main flash will light the image when your Powershot is really ready for it.
Good Luck with your search