This time I got a tiny bit more information from the MP kernel crash:

root file system type: ffs
cpu1: CPU 1 running
cpu2: CPU 2 running
cpu3: CPU 3 running
kernelkernel:                                kernel:   otection       trap,
protection                      netbsd:cpu_switch+0xc9: nop
db{1}> kernel:  rotect     ault tr    c       Faultection       trap     e=0
F   in  in                            con;inuing..    b{2}>ti    g..   db{3}>

Hitting CR at this point goes to the BIOS reset.