Just to be sure nothing simple is being overlooked, are you sure that the new speaker cables are connected with the same phasing? If the cable on one of the two channels has + and - reversed relative to how the cable on the other channel is connected, it would produce the symptoms you've described.
Also, if one of the XLR interconnects is miswired internally the same thing could happen. If you have a multimeter, check that pin 2 on one end is connected to pin 2 on the other end, and that pin 3 on one end is connected to pin 3 on the other end. If pin 2 at one end were connected to pin 3 at the other end (and vice versa), on the cable for one of the two channels, it would account for the symptoms you've described. If you don't have a multimeter, try reversing + and - on one of the speakers (or on an amplifier output) and see what happens; doing that would compensate for a reversal in an XLR interconnect.
Regards,
-- Al
Also, if one of the XLR interconnects is miswired internally the same thing could happen. If you have a multimeter, check that pin 2 on one end is connected to pin 2 on the other end, and that pin 3 on one end is connected to pin 3 on the other end. If pin 2 at one end were connected to pin 3 at the other end (and vice versa), on the cable for one of the two channels, it would account for the symptoms you've described. If you don't have a multimeter, try reversing + and - on one of the speakers (or on an amplifier output) and see what happens; doing that would compensate for a reversal in an XLR interconnect.
Regards,
-- Al