I thought I had some steelhead fly tying books that might add to the ones you mentioned, but, it seems the books you mention pretty well cover the current waterfront, their being extensively researched and vetted and all. Fusion is the name of the game now, I guess, with flies originally designed for Atlantic Salmon showing predominently in steelheaders' fly boxes, and, I assume, visa versa.
One book you might not have come across is Art Lindgren's _Fly Patterns of Roderick Haig-Brown_ (Lindgren, Arthur, _Fly Patterns of Roderick Haig-Brown_, Frank Amato Publications, Portland, 1993. ISBN: 1-878175-39-4). This is a slim little volume, but it might be of historical interest to you.