How do I get my Mac Pro to see the second monitor through a video splitter and/or switcher?

Question

In a recording studio we have a Mac Pro with two video display monitors in the control room and we want to be able to show the content of the second monitor to the person in the recording room on a big display monitor there. However, when we interpose a switcher or splitter between the computer and the second monitor so that we can (with a switcher) switch the second monitor signal from the control room monitor to the record room monitor or (with a splitter) split the signal to go to both monitors, we have no luck. On startup the computer does not see the monitor through the switcher, so it doesn't recognize its existence. If we start the computer up without the switcher in the signal chain, it sees the second monitor just fine, and (weirdly enough) we can then change the cabling to interpose the switch, which then works to switch back and forth between second monitors (control room and record room), but that cable swapping's a royal PITA. We want a simple solution that will allow us to start up the computer, see the second monitor in the control room, then choose to show it to the person in the record room with a simple flip of the switch (or even better, split the signal so it's available both places). The splitter we've tried most recently is this one: http://tinyurl.com/curen39 I'd appreciate any advice from people who have tried this configuration or something similar with success. We have a full ProTools HD Accel 3 system installed, so there's no room to install a second video card. Thanks.
Mac Pro 8-Core 2.4 GHz, OS 10.6.8

Answer 1

Christopher Dobrian wrote:
Thanks for the response! Yes, it's a 5x70 video card, a 5770 I believe. In any case, it does have the three ports, but (a not-well documented fact) that doesn't mean one can really get three full-resolution signals out of it at one time, as you alluded to in your message. So, yes, we did try hooking all three up directly to the computer, but the computer would only recognize two of those monitors, and the only way to get it to "de-recognize" the second monitor and recognize the third monitor was to physically disconnect the second monitor.
I did say when you want to connect three monitors to 5x70's there are some rules to adhere to.  These are covered in the first two apple docs mentioned above, or by title:
Mac Pro (Mid 2010), Mac Pro (Early 2009): Issues with three displays and multiple DVI, HDMI connections
Mac Pro (Early 2009), Mac Pro (Mid 2010): Supported display configurations
The general gist of these rules is that to drive three monitor son a 5x70 you need two active adapters.  That is why one of your monitors was disabled when you tried to add a third. 
Here's a good explanation of what's going in here and why you need two active adapters on these cards:
Active vs. Passive Displayport adapters *the truth*
If you use DVI monitors and any of them have resolutions less than 1920 x 1200 then you can use single link active adapters. The "AMD Eyefinity Validated Dongles" chart shows some active (and passive) adapters that are acceptable.  For example of a single link DVI active adapter is the Accell B087B-006B.  An example of a dual link DVI active adapter would be the one from monoprice.com if you need to connect monitors with a resolution greater than 1920 x 1200.
I'm doubtful that SwitchResX would be able to convince the computer that there were only two monitors connected and direct the second monitor signal to the correct place, but it certainly seems worth a try, so thanks for the idea! Any other ideas are still welcome in the meantime.
I'm not doubtful.  It is a very powerful utility for dealing with all aspects of multiple monitor configurations (they call them "Display Sets") complete with forcing EDID information if necessary.  The different configurations can be controlled with a (contextual) menu and/or hot key.
SwitchResX is academic at this point if you want to have all three monitors connected.  You would need to get that working first.  Then use SwitchResX to vary the configuration combinations.  So if you go this route the "name of the game" is figure out the active adapters you need.
I only described in general terms above about the adapters since you never said exactly what kind of connections these monitors require (single link DVI, dual link DVI, hdmi, mini-displayport, vga).