You should be able to get an LM386-based amp to work, but you may need more than just the chip. IIRC, that has a fixed gain of 20 that can be jumpered to 200, or vice versa. You might need some voltage control to get the signal to the right levels while keeping line noise low enough to avoid problems.
When you void a product warranty, you give up your right to sue the manufacturer if something goes wrong and accept full responsibility for whatever happens next. And then you truly own the product.