Retro Gaming vs Modern Televisions
The Ridiculousness
As a final note; consider the ridiculousness of trying to achieve decent video for low resolution sources that were never designed to run on a large, widescreen, high resolution TV. That in turn was never designed to support them, so has cheap (shite) low resolution analogue signal handling.
This is my current wiring for everything going into the amp (used as a hub) and TV.
Also, catering for the amp's woeful lack of HDMI inputs, we've a pair of Neet 3 way HDMI switches. I've used many cheap HDMI switches and these ones are the best by a million miles. They just plug in and work.
A final tip is to use the shortest cables where possible to minimise the spaghetti, because there's a lot going on here.