Thanks for the suggestion! I think i'll go with the THS7314. So just to clarify, i need to splice a VGA cable and then add the amp in the middle?
GPU output > vga cable *amp* vga cable > JPAC?
Yes. You'll still want the JPAC (or a video amp) to boost the signals to the 3-5v expected for an arcade monitor.
Even with the retrorgb instructions, I'd go a bit further than that and follow the diagram (figure 2) on page 6 of the datasheet at
http://www.ti.com/lit/ds/symlink/ths7314.pdfThis means putting both a 0.1 - 0.01uF ceramic cap AND a 22uF - 100uF electrolytic cap between 5v and ground near the Vcc in pin, as shown in that diagram. This will help filter AC interference from your power input.
I would also suggest adding termination resistors (75 ohm seems a good starting choice) onto the IC's RGB inputs, again as per that diagram (figure 2). Terminate them to video ground.
I am slightly concerned that the THS7314 outputs amplified video signals in the 0 - 2vp-p range (roughly doubled, 2V/V) so that it can supply inputs to 2 receivers at once. However, I think that the JPAC can handle those inputs and still give consistent outputs. I also note that between the 75 ohm load resistors on the video outputs, and 75 ohm termination resistors on your display or JPAC, you get a voltage divider that will cut voltage by half anyway. If you want to try to reduce the signal output levels anyway, you should try to do it at the inputs rather than the outputs. But I would just give it a go first.
Finally, I suggest you get a few of these ICs and the little PCBs, so that you can scrap and start again if needed.
Depending upon your skillz, you might want to try the AC-coupled circuit (figure 3) as well. Hopefully you have a range of capacitors and resistors lying around too.