Do you know how they are wired or have a picture of the wiring? Its odd that you have dual 4 ohms when the 5 channel would put out the most power with 2 ohms. Your options with dual 4's would be 16 ohms, 4 ohms or 1 ohm. With a dual 2 it would be 8 ohms, 2 ohms or 1 ohm. It seems to me a dual 2 would have been better for the 5 channel but the dual 4s would work better with your current setup. Maybe the gains were up higher on the other amp or the bass boost was on? Thats my best guess.

here are some examples
http://www.jlaudio.com/tutorials/wir...ex.html#2dvcsp