I have four of the above pws. I have four Canon speedlights and a old ETTL Quantaray unit also. I did a test a few weeks ago and substituted the quantaray in place of a canon flash and it fire ok I am not sure if it ratioed or not. I need to test some more to see for sure what it will do and not do. I have a st-e2 controller also. I am thinking since the speedlight is in ettl mode and all the ratio and firing is done through the pw unit that any ettl flash should work along with the canon flashes.

I am thinking that the camera squelches the flash in ettl mode so any of the 3rd party flashes could work in the same way as an Canon speedlight would. Can anyone more knowledgeable than myself comment on this.

if this is the case all you need is an Canon st-e2 or one of the master capable speedlights from canon and the the rest can be a 3rd party ettl speedlight.

Michael - I can tell you for sure that the FlexTT5 won't work on most, perhaps all, third party flashes in ETTL mode. I had a modern Metz 58 AF-1 that I sold to buy a Canon 550 when I moved to the Pocket Wizard setup. So I can't imagine your Quantaray is picking up ETTL commands. It may work in manual mode, as my Metz unit did. Just not ETTL.