And if you put everything back to stock, you still get no sound? I believe you mentioned the board monitor also doesn't turn on now?

Have you checked the 10amp fuse on the BM53 radio module in the trunk or has it been removed from the ibus loop entirely? It needs to be in the loop still for the DSP amp to turn on. If the fuse is blown, the amp won't turn on.

Also, IIRC, the board monitor won't turn on if the navigation computer MK3 or Mk4 is removed from the ibus loop. The BM is just displaying the interface received from the nav system. If you've removed the nav computer, you'll need to reattach it to verify the BM connections.