They compare quite well. There are differences, for sure, but they all have their strengths.
I think the LS6 and LS9 series are strongest on large scale music. They excel at classical orchestral music. The NX-Otica has an edge on vocals, smaller ensemble. Both do everything well, and most things excellently.
What's a fair price for a set of LS6's? In my opinion,$2750 to $3500 would be a steal, up to $4500 would be fair to good value. Up to $5000 I'd say you are getting your money's worth, but paying full price.
How heavy? Pretty darn heavy. It might take 4-6 men to lift and carry my LS9's