I have installed the dreamcast to the monitor now.
It was pretty easy, just cuted the cable that goes to pin 6 in the vgabox to get 15khz.
The vgabox takes like everything, even bangai-o now.
I Tried Virtua Tennis, DoA2, Garou and Cannon Spike, those worked fine.
My setup for now:

my Dreamcast connected to VGAbox that pin 6 had been cut off.

End of the VGA cable there is a jamma fingerboard that connects to a PCB switch and from there connected to the jamma harness and to the monitor.
So, when I want to use the PC I need to plug out the VGA cable from VGAbox and plug it in to the PC, but I will install a VGA switch, and I will install a switch to the PCB switch so I can install a Sega Saturn, so I can switch between 3 devices, or 4 if I connect another VGA device, so I can put in another VGA switch, maybe PS2, so I can play Contra Shattered Soldiers. What I know for sure is that, next time I play PSO online it will be played from the arcade machine.
My PC:
