Is there any other  benefit of the D9200 over the K7400? 
I use an ArcadeVGA and a Wells Gardner 25k7191 standard res monitor.  Windows and windows games will probably look a lot better on the D9200 as they don't have to be run in interlaced mode (but you said you don't care about Windows games).
Hmmm...  I would assume that vector games like Asteroids, Tempest, and Star Wars would look better because you can run in a higher native resolution without interlacing.  Also, medium resolution games like 720 should look better because they won't need to be interlaced.
Note that I haven't seen a 9200 in action, but I know that these are limitations of the 7191.
Also, does anyone know how the power is supplied to the K7400?
I use a plug that I cut off of an extension cord which I attached to an isolation transformer which is then run to the monitor's power wires.