Do you see "Super Pocket Download Mode" in Device manager with it connected in flash mode?
I would only bother testing with the bootloader you found marked as being specifically for the Super Pocket.
Don't use the GUI "RKDevTool" you need...
You need to start with rkdeveloptool db {your_bootloader} and then after that you can test with rkdeveloptool ppt to get a partition list with the starting LBA for each partition. if loading the bootloader hangs, you don't have the right...
Here is the help info from the Windows version of rkdeveloptool. the commands should be identical regardless of your PC OS.
Everything aside from WRITING and ERASING would be 100% non-destructive/safe to experiment with.
Based on OPs post, it seems the goal is an easy solution for a large flatscreen TV that doesn't involve any cutting/irreversible modding because it is a sought after model due to the audio.
This is what I use on one of my PS1s: https://www.amazon.com/dp/B07MYVF61Y
IMO is is much better than the POUND version which I used to have. It also works on PS2 and supports RGB mode there.
In another I installed a PS1 Digital, which is not...