Hey, good news. As you'll see below, something is different. I'm not sure what changed from yesterday, but the images below are using soft15 with the sync lead from the jamma harness connected to both V and H/C pins on the connector. (Now if I can just get Advancemame sorted out, I can get them all sized for the screen - although it's probly that polarity parameter I have to find.)
The only thing is the monitor is not quite as bright as I thought it was with the jamma board connected, but I could be wrong. I did turn with the color and brightness, but they seemed to be adjusted for the best already and I had to hunt a little to get it back to where it seemed it was. The last image is pretty good, but I turned up the brigtness in mame to 1.15 .