check what kiwi is saying

we once did a 6 live input SD-SDI with 3 phoenix cards on a 2009 macpro but with 10.6.8 and a flashed GTX285
the tearing only occured when the server couldn't handle all the HD-SDI signals, meaning 5x SD and 1x HD-SDI instead of the 6x SD-SDI

all video inputs where isolated aswell
do you have everything grounded on the same cirquit?

does it also occur when there's only 1 input active?

did you install the GTX drivers by setting it up with a GT120 first time?