Tiamat 7.1v2 -- Center channel playing in right ear only?

Tiamat 7.1v2 -- Center channel playing in right ear only I encountered this on two systems, both using Sound Blaster cards. (Old: Recon3D, New: Sound Blaster X AE-5) On the Recon3D I was able to "disable" (?) the center channel and everything worked as expected. On the AE-5, I don't seem to have that option. On the control box, all channels are set to max volume. Master is 50%. 7.1 enabled. All connectors have been seated and re-seated. All channels are enabled in Windows speaker config. Nothing is set to full-range. If I disable 7.1 mode (from the control box), I get only front left/right as expected... but if I crank the volume to 100%, I can just barely make out the test tones being played on all the other channels, including the center channel to both ears. Setting Windows to stereo instead of 5.1 works as expected. I don't know if the hardware has simply always been broken and because I worked around it in the beginning I didn't pay attention, or if there's a config issue that I'm missing somewhere.