I'm not a video engineer so not sure if i will explain it correctly but i will try. But yes, this applies to all PC Engine and TurboGrafx systems.
The standard RGB signal is 0.7 volts. After amplification on the THS7314 or NJM2267 (both are 6dB amps), this is what the output of the console should be sending to the monitor as it is what it is expecting.
http://www.syncblaster.com/RGBfaq.htmlWhen you amplify the SNES or N64 with one of these amps it produces 0.7v, but when amplifying the signal from the pc engine it is 0.8v. So the voltage being too high will make the picture too bright. I have not actually measured it myself, but the output of the PC Engine RGB lines should measure around 0.4v before amplification and on an N64 measure around 0.35v.
http://www.sengpielaudio.com/calculator-amplification.htmThe reason the output resistance was changed from 75 ohms to 100 ohms was to compensate for this. Doing it with the 91 ohm (with 470 ohm parallel to ground) makes it appear to be around 75 ohms to the monitor. Before this amp was not taking into account that the monitor is also expecting 75 ohms along with 0.7v. This new design corrects that. Although the 100 ohm resistors on the output were not going to damage anything.