I am not too sure on the issues with triggering the 580 but it definitely sounds like a sync speed issue. What shutter speed are you using? The popup flash will not allow high speed sync so you will be limited to shooting at a max of 1/250th. What sort of studio trigger are you using? Unfortunately the 580 will not work with IR triggers (apart from Canon's own one) but I use mine with a set of cheapie radio triggers. If you have time before he event it might be worth looking into getting a set as they should be able to trigger any of your lights. Or could you use a single trigger/receiver to fire the 580 and slave the other lights off it.
As for the issue with creases the easiest solution might be to push up the power on the light on the background and blow it even further. Depending on the depth of creases this might be enough to blow any shadows that they cause, if not it will just be a matter of dealing with them in PP which shouldn't be too bad. If shooting groups a bigger problem can be people falling of the edge of the BG which can lead to a lot of work on the computer and is definitely best avoided.
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