I did a little research and came up with a way to add an amp and sub while still being able to control subwoofer gain from Head Unit.

First: Remove fan cover top panel beneath glove box on passenger side by pulling down and towards you. Then remove right side kick panel on pass floor( in front of door).

Second: Inside you will see the Stock Amp.(very shiny silver). There are two plug connectors on the bottom of the amp. The plug closest to you is the output (wires go to all 6 speakers correspondingly). The plug closest to the front of the car, furthest from you is the Input ( wires come from Head Unit w/ signals). Unplug the input Plug connector (20 pin connector).

Third: On the input pin connector the subwoofer positve low-level signal wire is RED w/ BLUE STRIPE and GRAY BAND. Splice (do not cut wire, just splice) and connect a wire, then connect new wire to positive input on amp.
The subwoofer negative low-level signal wire is WHITE w/ GREEN STRIPE and GRAY BAND. Splice and connect a wire, then connect wire to negative input on amp.
The Remote turn on wire for stock amp is RED w/ YELLOW STRIPE and GRAY BAND. Splice and connect a wire, then connect wire to remote turn-on on amp. Reconnect Plug to stock amp.

Fourth: Connect Positive and Negative Power supply to amp.

Fifth: Connect Sub to amp. Enjoy!!!

By connecting to the signal level wires before the stock amp, this allows the head unit to control how much gain (power) the amp produces. Enabling you to control Bass levels with the Head Unit (in sound menu with subwoofer control, -6 to +6).

I used Basslink so the amp and sub are one unit. I also left the stock subwoofer connected which allows me to have both running at the same time (works if you left sub wires connected at stock amp and just spliced into them). Sounds GREAT!!! I have the sub setting just under half (-1) and it produces enough bass to feel the music as well as hear it. Turning the bass up all the way and I have enough bass to shake the neighborhood.

 

Sounds like a good job! Too bad that NEW basslink won't fit. We have the older style in our Accord, haven't decided what to do with the TL yet.

 

I used the small 10" basslink. I didn't want too much trunk space taken up. This was the perfect match of bass and space!