The TH2G-Digital does DVI to analogue conversion internally.

Disconnect the 3way working one and connect the other just to program it and test it. Also worth downloading the new software from the matrix site if not already using it.

Once you've configured the new one - then reeboot and re connect
Always try to do one thing at a time...

I assume that you've tested the projector on a working output anyway...

DP supports analogue - so long as you use an analogue adaptor. A passive DVI-VGA adapror connected to a DP-DVI adaptor won't work...

The TH2G will also remove HDCP, which may be the problem here - so the gefen DVI-VGA converter may not be required in this scenario - unless you want to use the 'parrot + gefen' solution instead

S