It could be that the lpad is defective. Try wiring around it and see if you're happy.

Can't you adjust the balance between the sub and the backbox speakers?

Well I mean removing the lpad from the circuit. It should be if you turn the lpad all the way counter clockwise it should be like its not in the circuit and all the way clockwise it lowers the sound from the backbox to almost zero. In mine I have to have the lpad pretty far clockwise to get enough bass. If you can barely hear the backbox speakers, likely the lpad is defective or wired up wrong. The original speakers aren't even coax and do not put out better sound.

Yuriijos,

Sometimes tweaking the system to your liking can be a bit confusing. Markmon is onto something, but to take the control out of circuit all you have to do is turn it completely to the right. This will put full machine power to the back box. Though we have the occassion bad lpad, We test everything prior to shipment and they never make it out the door. Usually we find this issue to be an adjustment. The crossover only effects the subwoofer itself, not the back box speakers. Low sound from the back box is all in the back box control. I will pm you some pointers on adjustment, and feel free to give me call, I will gladly walk you through it and get your AC/DC sounding great!

Greg