Hi xga,
That's not JPAC's fault but your video card not detecting the arcade monitor. Probably your tri-sync did load the RGB lines with 75 Ohm, but the MS9-29 doesn't. The easiest method is what you're already doing: DVI->VGA. The DVI works because although it doesn't detect the monitor either, it's the default output so the video is routed through it. Other solution to actually trigger detection is to add resistors between the RGB lines and earth (75 Ohm value is recommended in many places, but in my experience it produces a very dim picture; 270 Ohm still works and doesn't cause a visible brightness drop). Finally, Windows 7 Emudriver is patched to force detection.