I can't really answer your question since I haven't studied the Sämisch nearly as deeply as I want to... yet. But I have many books on it and have played it quite a bit. I always get interesting games. It's the kind of rich, unbalanced opening I would be happy to play with both White and Black.

Based on my impressions so far these are the sources I would prioritoze:

* The Opening Repertoire book by Eric Montany - for 6.Bg5, which I dabbled in even before that book came out

* The Principled Queen's Gambit Part 2 (Chessable course) by Daniel Barrish - for 6.Nge2

* The Sämisch volume of the King's Indian series by Kotronias - for an extremely in-depth view from the Black side

* The ChessPublishing King's Indian section - for ongoing developments

I haven't been that much into the traditional main line 6.Be3, but there is a decent older repertoire book by Svetushkin (ostensibly on the "Anti-Grünfeld") that covers it. I think maybe the recent book by Cheparinov has 6.Be3 too, but I'm not sure - haven't seen that one. But Cheparinov is known as a strong theoretician, so it's probably good.