Suggestions fol keyboard sharing?

I have 2 Mac Pros (10.7) connected via LAN and I would like to share a keyboard between the two.

Here's the tricky part: I need to be able to press the space bar and have it work for both at the EXACT same time, and do this reliably, multiple times.

For this reason it's also important to be able to turn the keyboard sharing off when I am not using it.

I have tried Teleport and have looked into Synergy KM as well, and for both you need to switch between computers and control one at a time. The thing that sort of worked was the built in screen sharing feature, but this is very clumsy and hard to control since I am running 5 projectors off of each computer. The ideal for screen sharing would be to be able control the main displays of both computers and have it STAY that way, without having to hover my mouse over the screen for ever and ever. The resizing and moving of the screen sharing display is also very clunky with multiple displays.

Does anyone have any suggestions, either for making screen sharing easier to use or using another software/combination of softwares?