Off Camera Flash with E-TTL

I apologize if this question has been asked previously but I searched and couldn't find an answer.

I have a few 580EX speedlites and I'd like to use two of them off-camera as key and fill lights while still maintaining E-TTL functionality.

Is the following scenario possible?

1. Set lighting ratio on Master/fill light
   
2. Mount Master/fill light on lightstand using an ETTL cable from FlashZebra's website (I'm thinking of either the 5 or 7.5 meter cables)
   
3. Mount Slave/key on second lightstand and trigger wirelessly.

The only issue I see with your setup is if you actually have the 580 EX, not the 580 EX II. The fact that you can control a 580 EX II master from the camera (provided the camera is new enough; at least a 40D) may come in handy when the master is a bit away from the camera.
When it's on camera, it doesn't matter that much.

You raised a point I did not think about at all.

I don't have a "new enough" camera; currently I have a 30D, a 5D, a 1D Mark II and a 1D Mark II N but I plan on acquiring a 1D Mark III sometime soon.

Last year I decided to rationalize my flash setup and sold off my Nikon SB-28 flashes and CyberSync triggers. I settled on using 580EX flashes over the later model because from what I've read a number of the controls on the EX II have been moved to the menus. But the ability to control a 580EX II as an off-camera Master directly from the camera would be a huge plus.

apersson850 wrote in post #9307147
The only issue I see with your setup is if you actually have the 580 EX, not the 580 EX II. The fact that you can control a 580 EX II master from the camera (provided the camera is new enough; at least a 40D) may come in handy when the master is a bit away from the camera.
When it's on camera, it doesn't matter that much.

The "number of controls" that have been moved is the mechanical Normal - Master - Slave switch. Since that setting, just like everything else, now can be controlled from the camera, a mechanical setting on the flash wouldn't work. That can't be controlled from the camera.

The loss of this switch makes it difficult for users who frequently want to switch quickly between normal and master mode.

On the plus side, the 580 EX II has:

• Faster recycle time.
  
• Control through the camera's menu system.
  
• Its own sensor, if you want to use the old type of automatic flash.
  
• Better battery compartment cover.
  
• Better locking system when mounting on the camera.
  
• Sturdier foot.
  
• Built-in sync connector (not sure if that's on the 580 EX as well?).