I've done this to a few other TVs, but I've wanted to have a go at a very nice Trinitron set for a while (KV-27S42). After seeing someone's youtube video where they got most of the way there with this particular set, I picked one up on Craigslist for free to try it. It's a beast! It's "only" 27" but the tube is phenomenal.
In short, I've got it working - I spliced in RGB to the OSD mixing circuit as most people do. The outputs come off the microcontroller and go through three resistors. I used a four position switch to go between the OSD outputs / blanking signal, and my own.
For the input stage, I terminated to ground with 75 ohm resistors, and fed my RGB input to a THS7314 triple amplifier (the common one popular for N64 stuff). After that, 75 ohm resistors went in series to the TV PCB for OSD mixing.
The image looks great! I used the service menu to move the image as far to the right as possible, to account for the lack of sync delay (most TVs align their image expecting the composite decoding delay to make up for the difference).
There are some tiny tiny quirks I have to work out, though. For one, convergence needs work in the top-left corner. Not a big deal, I've had to do it before.
The more annoying quirk is that the RGB signal comes so much earlier than the TV expects that it ends up having visible image data during the front porch. This makes the Jungle chip clamp to the image colors, which then subtracts that color from the remainder! This is a problem for a lot of older games with large borders that aren't black, like NES games or Genesis games at 256px-width. Fortunately, Genesis at 320px (H40 mode) doesn't have this issue. To correct this I have an Extron device on the way which can delay sync for an H-Shift adjustment.
The final problem is a little more odd. Similar to the clamping problem, some systems will have the color balance change slightly based on what is on-screen. It is as if the more a color channel is being used, the weaker it gets; on the Street Fighter 2 character select screen, almost all of the blue is gone, or in Super Mario Bros, the sky is not so blue and every object looks a bit yellow tinted (missing blue). The problem is not limited to blue, but those are the best examples.
What I think is going on is that the affected consoles (RGB NES, SNES, RGB amp'd PC Engine) have capacitors in their output termination, and these caps are maintaining a small DC average of the frame, which is throwing off the clamping circuit. The Genesis doesn't have these problems at all, and when I pulled RGB from that, I just have 75 ohms resistors in series coming off of the CXA1145 and nothing more - no 220uF capacitors. I wonder if a cheapo fix would be to remove the output caps on the affected consoles.
Anyway, as I make more progress I can share more about what was done, and maybe provide a reference for anyone wanting to do something similar. This is a very common and very nice CRT set from 2001, so if it can be given RGB it's a great alternative to a large-format studio RGB monitor.