Canon S80 with external flash?

How does the S80 control the total flash output when an external HF-DC1
flash is used?

The reason I'm asking is because I want to know if other external flashes
can be used with S80. I already have canon's 580ex. I also have generic
handle mount flashes (from the old days).

It is too bad canon doesn't make a version of S80 with hotshoe. The G7 is
not useful to me because it is missing the most useful feature of the S80 --
28mm eq. wide angle. Having to add a lens adapter doesn't count (it may ruin
the telephoto end of the zoom, and adds lens distortion..)