I just picked up a 2003 TL-P, and i want to install a box and amp. Crutchfield says that its very complicated and that i would need to tap into the speakers in the doors instead of the sub in the back. I was planingto disconnect the sub and wire the new amp and sub. Is this possible, is it recommended? can someone please advice. Thanks,

 

Speakers in the doors are already receiving a high-pass signal from the Bose EQ, so tapping into those won't work.

Some people tap into the stock sub speaker and are happy.

More work is to tap into the preamp signal going into the Bose EQ (coming out of the HU)--but that requires taking apart the dash, cutting into harnesses, and soldering.

I think your original plan would work and be fine. Be aware that you'll get automatic loudness, which will turn up your sub at low volumes.