Well bough the B-2 and B-2x are 26kg or 57lb 3oz, so that would be a tie
About the construction of the MX-10000 we really need Unda to explain this; it is properly the most complicated amp ever to come from Japan. But B-2 you are right and not

, I believe the 10000 is closer in design to the B-2x than the MX-1000. The thing is Yamaha took the best ideas from earlier designs, put it all in a tub added a few improvements a lot of yen, stirred it around and out came the MX-10000.
One of the key things in the 10000 is the class A circuit witch comes from the B-2x, if you look at the diagram I posted before the you see the speakers are connected between the class A stage and the A/B output stage, where normally they would be after the A/B output stage. The Yamaha engineers really did amazing stuff in designing this amp :ntwrthy: