Blown channel on bg radia bgx-a2 sybwoofer amp

My theater uses four bgx-s12b subwoofers that each use twelve 4" opposing speakers. One of the bgx-a2 amps two channels died "unrepairable" and the amps are rare with BG Radia out of business. Unfortunately the amp contains the circuits that balance the output of the speakers (which peak at 110 Hz when powered by a normal amp). I cannot find a used BGx amp. Solution ideas?