I've got the same problem with the update.
Doesn't boot and both displays are blank.
My system is A1200 PPC603e/68040 64MB MediatorLT4 (Voodoo3, SB128, Ethernet)
My 3.5 HD and CD are connected through a 2.5 to 3.5 DIY cable.
If I understood correctly, you replaced a similar cable with an Elbox IDE interface and it worked for you?
Any ideas, for people who don't own such an interface?