[kaigoss69]

It sounds like you don't understand what the Technic harness does. It does not change frequencies. What it does it taps the output of the OEM amp that is going to the underseat speakers. The frequency range for that output is about 30 to 150Hz. The signal still goes to the underseat woofers, so they play 30-150Hz. The harness piggy-backs off of the underseat speaker signal and feeds a low-level signal (30-150Hz) to an aftermarket amp for a trunk sub. Then you would normally need to filter out the mid-bass signals (about 80-150Hz) using the trunk sub aftermarket amplifier so that the subwoofer plays only the frequencies it is intended to play (30-80Hz in this case).

The underseats are still getting a 30-150Hz signal from the OEM amp but since you replaced them with Earthquakes, you are missing some of the mid-bass that the OEM woofers originally played.

In order to do it right, I believe you should re-install the OEM woofers and run them band-passed between 80 and 150Hz off an aftermarket amp. So you would need to do two things with the wiring:

1.) split the signal coming from the Technic harness using the amp crossovers into 30-80Hz going to the sub amp and 80-150Hz going to the new amp for the underseats.

2.) cut the wires inside the Technic harness that go from the OEM amp to the underseat woofers. Then connect the end that goes to the woofers to the new amp.

The OEM underseat woofers will do fine with 50-100 Watts so choose your 2-channel amp accordingly.