Sub/Amp on Bose in Mazda 6

I have a 2003 Mazda 6 with a bose system. The bose system has a factory sub in the trunk with four wires going into it. I have an amp/sub combo that I want to install. I bought a special line output converter piece from soundgate (model LOCB.2) to do it. Out of the four wires that go into the factory sub, one shows 12v, one shows ground, and there is two more. Are these the preamp wires? I am just looking for some suggestions for anyone with experience in adding amps onto bose systems.

Can anyone help me out?

your on the right track, the wires going into the sub that don't have voltage are the signal leads, you should be able to use these for your signal wires. Depending on your amp\sub, i suggest disconnecting the factory sub (disconnect power to the amp or you can get a wierd feedback.