Disassemble Asmedia USB 3.0 Bridge Board Firmware?

I’m trying to disassemble the firmware binary in an Asmedia USB 3.0 bridge board based on the ASM1153(E).

Through initial research, it seemed that the op codes would be something like the x51 instruction set. But this does not appear to be the case.

If anyone has disasembled Asmedia firmware from one of these bridge boards, please give me a nudge in the right direction.

My goal is to add 4k sector emulation, which the old Asmedia bridge board firmware often has, but no public versions of the newer ASM1153(E) firmware seems to have.