After a few unsuccessful attempts, I was finally able to do a reasonable job at soldering a 6-pin header in one of my URC-6800. I must admit that I had done quite a mess in this one, even cutting one of the traces leading to a JP1 hole. I finally got a 6-pin header well soldered and I was able to repair the trace with Quick Grid Rear Window Defogger repair kit (highly conductive paint) that I had bought to repair worn buttons on my second URC-6800.
Now I am able to use not only my simple interface cable, but also the serial one that I built in the first place to free up my parallel port.
Now I am really enjoying JP1.
Thanks to all the JP1 experts!
François