BKK-BRU will be operated by the 777-200ER. The seats are identical to the seats on the 773 except one thing: 773 seat is arranged 2-3-2 with middle seat while 77E is arranged 2-2-2 with no middle seat. If you fly on the 773, be sure not to get stuck in that middle seat.

I would not suggest you to go via MAD. MAD is unreliable in terms of the aircraft type. Sometimes you'll get the notorious "7442" config with very out of date cradle business class seats.