Dan, on any "Varnish" type finish that I have had to re-finish, I strip it first with a "Jerry Fisher" scraper, then I sand it with 400, then I apply some sort of Citrus stripper, then another light sanding before staining, if I decide to stain....even when I do stain I sand again with 400, then 600.
I have a complete set of Jerry Fisher Scrapers, so there is no nook or cranny, even checkering up to 20 lpi, I can't get to.
If you would like to borrow them I will gladly send them to you.