I tried doing the thing, and I ran into issues. Here's what I did:

- I changed my makeshift plug, the one that plugs into the former speaker wire connector receptacle at the bottom left of this photo. I modified it so that it contained only the R+ and L+ wires at the receptacle. The dangling R- and L- were tied together and connected to the ground plane of the TV's circuit board at the screw hole that's seen to the left of the receptacle in the same photo.

- I solder blobbed back over the joints that I had scraped away on the Russound ADP 1.2 so that it no longer had separated grounds, and was back to its original design.

- I left my modified voltage divider resistors in place on the Russound: R1=10k 1watt, R2=47ohm 1watt. This ratio gives a Vout that's about 0.5 of a percent of Vin.

This produced output which was super quiet compared to the previous configuration, unusably quiet. I thought that perhaps maybe everything was working as intended and maybe the only remaining issue was that I'd changed the ratio of the voltage divider too much with my earlier experiments. So I tried this:

- I put the original resistors back in the Russound, which was R1=3.9k 1watt, R2=430ohm 1/2watt.

This produced scary results! Even before any sound was played, simply turning on the TV caused a noisy hum out of the line-level outputs. More than just a 60cycle noise floor issue, this was a massive buzzy hum like something was wrong. I turned off the TV and put everything back the way it was: Re-separating the grounds on the Russound voltage divider and re-connecting all four wires back to my makeshift speaker connector plug. This made things go back to normal.

I also tried different resistor values, trying R1=6.8k 1watt, R2=68ohm 1watt. This is supposed to produce Vout at about 1 percent of Vin. This does pretty well sound-wise.

Because of your warnings, I don't want to shorten the life of that TV's board. I checked the temperature of the two transformers and the audio amplifier chip just above them (left center of this photo where the white arrow is pointing). I checked with my fingertips in several situations, such as playing music softly or loudly, or having the volume set at zero, and also swapping between plugging in the Russound voltage divider and plugging in the TV's built in speakers. I found that in most cases those transformers and the audio chip get pretty warm to the touch, getting warmer as volume increases. I don't have a quantitative measurement but I think that using the voltage divider makes them noticeably hotter at the same volume settings, but not by a huge scary amount. Still, it was warmer enough to worry me a little, so I've disconnected the Russound device and gone back to just running my self-powered monitor speakers from the TV's headphone jack for now.