Avionic, I make a distinction between hot running "consumer" grade Yamaha's and models that are built to a higher standard like the M-2, B-2, and presumably Mark B's BX-1's.
I'll give the BX-1 the benefit of the doubt. Looks like there is enough shielding inside and the boards and components are robust enough to take the heat. Hopefully, Yamaha spec'ed 105 degree caps.
All of the caps are 85 degree Elna's & nichicons..