I just got my JXD S7800A in the mail (they were supposed to have sent me a S7800B instead, grrr) and decided to have a go at this and follow your guide.
Needless to say it worked right off the bat, and now I've paid for Amiga roms twice in my life ha ha, though I know I could have moved them over manually.
Anyhow, I set this to 28Mhz instead, and so far so good. I've only ran Montezuma's Revenge and Alien part 1 thus far, but will continue testing and see what all I can get it to do. Though to be honest, under emulation, I generally only game as my real 1200 suits me just fine, though it still needs sent up north for recapping.
So what am I saying after all of this? Oh yes... Thank you, thank you very much! I love this guide and that emulator, both are easy to use and follow.