EDIT: You don't need v11 if you aren't playing The Sellswords or Back to Brynnlaw.
If you are planning to play these mods with Xan's commentary, just install v11 over. If not, don't bother.
I'm not sure how tragic and happy endings work together in the same game storywise.
But you can also do the tragic ending, reload, and do the happy ending, with all new v11 SoA content and ToB content.
(If Xan dies in SoA, you'll have a few variables to correct to romance him in the same ToB game).
But tragic content in ToB(dreams, Valygar's talks, consolation talks from Keldorn and others) remains the same in v9, v10, v11.