LFE = your subwoofer
SB = Surround Back for 6.1CH movies/TV programs.
If you are using a 5.1CH source, the speakers used will be:
FL (front left)
C (center)
FR (front right)
SL (surround left)
SR (surround right)
LFE (low frequency effects)
for 6.1:
FL (front left)
C (center)
FR (front right)
SL (surround left)
SB (surround back)
SR (surround right)
LFE (low frequency effects)
Hope this helps!