Re: URGENT! 7600CS (rev 02e1) stays black when screen via VGA extender
You've already forced the driver into a state where it doesn't talk to the CRT. That is the root of the problem. What you need is to provide the driver with a modeline which the CRT can use. Alternatively, you can use the CustomEDID option, once you've captured the EDID. See the driver README for more details.
I should note that the above would be specific to one model of CRT. Also, from your information above, it sounds like you're using DFPs, not a CRT. That further complicates things as the acceptable modes on a DFP are significantly more restrictive than what a CRT would accept & work correctly with. Are you running these DFPs with a DVI-D cable or an analog cable?
However, none of the above may work if the problem here is a signal degredation problem due to the length of your VGA cable. It should work for the KVM, assuming that you're not using excessively long cables.