>>28452858 (OP)>If I spliced in a second oem ampSpliced in what way?
In series? If you feed an amp with a pre-amplified signal it's probably going to shit itself. Unless it's an amp that's designed with high level inputs, which most OEM amps are not.
In parallel? It's going to sound like complete garbage because you'd be mixing 2 signals together that are almost surely not going to be precisely in phase with each other.
Just cut the OEM amp out and put in a more powerful aftermarket amp.