B11 is a combination tuning. Part of it is A6 and the other part is B7, B9, B11.
Strings 1 through 4 are an A6 chord.
The middle strings (omit string 1) are B9 (and B, B7, B11).
Fret 2 is B6, and Open is B9. Whatever 6th chord you are playing, just drop back two frets for the 7th or 9th chord. For example, A6 on fret 12 (strings 1 through 4), drop back to fret 10 and play the middle strings (omit string 1) for A9. That big 9th chord is the basis of songs like "How D'ya Do" and "Sand".
Check out my tab below to see one way to play a I, IV, V pattern on B11.
The chart below shows some of the open chord positions, with root note A, root note F#, and root note B. There are other open chords that I left off the chart... a diminshed chord on strings 3, 4, 5. Also Am6, flat 5, Aadd2, etc.
UPDATE: Here's a demo of B11 sounds I made a couple of years ago ---> https://www.youtube.com/watch?v=a0642tjWXrg
