I finally invested in radio triggers for my flashes. So this image is from my first assignment with the new triggers.
When using the flash off-camera you can either use a cable, infra-red or radio signals. The spiral cable that also transmits the aperture, shutter speed and ISO is simply not long enough. The next option is a longer cable but then you in principle need to set these values manually on the flash.
You want flash 2 to communicate with flash 1 and I set that connection up with infra-red signals.
Then the cable won't work and your soft-box is in the way of the infrared signals. You name it.
This was the point where I was ready to invest in radio transmitters. Strobist recommended PocketWizard Plus II set but Interfoto told me they would not be importing them anymore so I invested in a PocketWizard MiniTT1 and a PocketWizard FlexTT5 instead.
With using two flashes you really scould have two Flex'es - one for each flash.