2003 Trailblazer with Bose amplifier

In all the cars I've ever owned, I've never kept a factory head unit.  I've always put in an aftermarket CD player and added a subwoofer.  For many reasons (OnStar, steering wheel remote controls, 6-disc changer, Bose speakers), I have decided to keep the Bose head unit and just add a subwoofer using a speaker-to-line-level converter.  I did this using the speaker wire connections at the Bose amplifier in the passenger-side rear panel.  It worked... except the levels seem to be too low... this even with the output on the converter and the amp gain turned all the way up.  I haven't tested the leads yet with a meter to see what kind of output i am getting... I thought I would see if anyone else has already done this with the Bose amp and had any suggestions.  Thanks.

hey chilljoe, why dont you just tap the wires from the head unit? You can find the diagrams on google.ca Just tap into the wires from the head unit and connect the in the speaker level inputs, done deal! You dont need to use a converter or watever that is!