Elph, dude.

Elph.

Bob,  Digital cameras have unique needs in external flashes due to the
pre-flash they use and other factors.  I don't know your camera or housing,
but someone on www.digitaldiver.info will know about it most likely.  The
Ikelites are good strobes.  I use a DS-125 on my Olympus, but it won't do
you any good if it won't trigger on your camera.

The Elph might be ok - I'm not sure if the preflash problem applies as my
S400 has the focus light.  But they are pretty close to each other and
you still have to bounce the light up.  In any event, since you already
have the Aquastrobe, it doesn't cost you to find out.  For simplicity, you
might use a pool at night first.  And if it works, tell us.

Otherwise, there are solutions from Ikelite and others with a fiberoptic
cable that run 400-500, I think.  I've not gone that far yet, but eventually,
maybe.  I'm not convinced the elph is a great choice for UW photo.  Great
above, but limited below.