cant use display link at 50hz

[rodrsamuel]

hi every one,

i´ve bought 4 startech usb3dvipro with dl3100 chip
and i cant take out 50hz resolutions out of it, only 60hz I'm an video artist and i need to connect my computer to video projectors with vga cables, and stay in sync with cameras (im in europe so the standards here is 50hz 25fps video)

the main resolutions i need are:
-800x600 50hz
-1024x768 50hz
-1280x720 50hz
-1280x800 50hz
-1920x1080 50hz

i have switch resx but even with that i didn't find an way of resolve this
my osx is montain lion with a mbp 15"retina

thanks in advance for all the help you can give me