#5: could you reduce the number of strings behind to 5 (to match the number on a note sheet), and also play a little with the typography for the S and the B?
#10: has to much going on inside SB I'm afraid.
I like your playfullness with #8, #9 and #11, but I need to let them sink in a bit first :-)
#12: hmmmm, try removing the lines and enhance "SB" to the same size as "STAGE BACKLINE" so that "STAGE BACKLINE" becomes an informative under text, and that "SB" can be used alone if we have to little space on the flight cases (for the musical equipment).
#3: can you emphazise a bit on STAGE? Could be made to appear as if "STAGE" was the logo part, and "BACKLINE" was the informative undertext. Made as a pure text logo. Play a little bit with different positions and angles on the two words?