loaked

I have a 2006 E350 with the HK logic 7 sound system. I was wondering if the signal going from the HK amp to the door speakers was a full range, or if it is crossed over. I am adding an amp, and was going to tap into those wires and send them to a 4 channel, and use the preout on the 4 channel to a sub amp. But I dont want to do that if the signal has bass cut off on it you know.

I was thinking of tyring to find a bass cd with certain frequency's on it, but even then if it is crossed over it will still play frequency's under the crossover point a bit. I was hoping someone on here would know, even though its a pretty niche question.