Sub is weak

[Anthonyb]

2008 GMC 2500HD with Stock HU/XM onstar. I have replcaed both front and rear speakers and running them from a 250 watt 2 channel amp. I used the front speaker outputs from the HU to drive a 250 watt amped bazooka tube but I am getting very little base. The tube has a high level inputs, so I used those from the old front speaker wires instead of the RCA's. Could the HU be sending too weak of a signal to the amp? Would I be better installing a line out converter and using the RCA inputs? I am thinking about using a 2 in 1 RCA adapter and tapping in front of my other amp but that would mean everything is run from the rear speaker channels of the HU. Is this a problem?

[Cablguy184]

line out converter or replacing the HU would help Sir ...