Thanks for the post. I just bought a Vivitar 5600 off eBay and I have just started to play with it. It looks good!
There has been so much confusion and incorrect information about using older flash units that have higher voltage than 6 volts. Here is a thread I started back in Sept. 06.
Apparently there are many who still think that the allowable sync voltage on the hot shoe of the Rebel XT is only 6 volts. THIS IS NOT TRUE! I also bought the safe sync when I bought the my XT, and now I find that I do not need it on all of my flash units. These include Vivitar 285 HV, Metz 60 CT1, White Lightening Ultra, and Speedotron studio units. I finally called Canon and talked to Todd and told him that I had read that Chuck Westfall, the director of media and customer relations had said that all the newer cameras have electronic sync circuits and they all allow up to 250 volts at the pc and the hot shoe. These include the XT, 20D, 30D, 5D, and all the 1 series. Todd confirmed that this is true. Off comes the safe sync. The crappy thing does not have a way to tighten it, and it has a way of becomeing loose and losing contact. GOOD RIDDANCE!