Can someone with a 580EX II answer a question for me?

I am wanting to run a 580EX II off camera in a soft box using an E-TTL extension from the cameras hot shoe. I want to put the 580 into master mode and use it to trigger a 430EX II behind my subject. So if you have a 580 can you either test or tell me if a 580 in a softbox can still trigger a 430?

Sure it can.
But depending on the conditions, it may need line-of-sight. This will be much more of a problem outdoors.

I've triggered slaves inside a softbox, so i suspect it is possible to trigger slaves with the master in the box

What all does the 580EX transmit to the slave? If I change menu settings on my camera for flash control will it take effect on the slave as well? Such as changing it to manual mode or anything like that.

Ratjack wrote in post #14508939
What all does the 580EX transmit to the slave? If I change menu settings on my camera for flash control will it take effect on the slave as well? Such as changing it to manual mode or anything like that.

You can use FEC, FEL, HSS, stroboscopic, and modeling flash. You can switch to manual (slave must be in E-TTL initially) and adjust manual output.

You can't change channels (obviously), change zoom settings, change custom functions, use second curtain sync, or adjust power in free-agent wireless mode.