One of the challenges is that DVI is a 50 Ohm terminated signal that is quite sensitive to reflections and such: it is typically not a good idea to try to split or branch a DVI cable to two receivers because they will get half the signal power each.

I'm trying to design the "VSYNC sniffer" to be high-impadance input, which is normally a bad move for DVI as it causes reflections. But, if we put this sniffer right at the source (the graphics card), reflections shouldn't be much of a problem. That way, the signal going to the monitor/beamer shouldn't be degraded much by adding this sniffer in.