@Jean - Maybe I am missing something here?
(1) Download your ebooks to Kindle For PC ... if you haven't already (think you did).
(2) Load them into Calibre from the 'My Kindle Content' folder (User Documents).
NOTE - If you want a little help to determine what file is what and even do the importing for you (with or without DRM removal), then maybe get a copy of my
AZWPlug program.
(3) Once in Calibre then Send them (DRM versions) to your K1.
(4) Once there, Sync your K1 to have them verified.
I haven't tried Steps 3 or 4 myself, but from what I have read elsewhere, that should work.