So I've followed your instructions and Bi-Amped the TL260's today. I can't tell about sound quality, but the speakers are obviously louder than when single-amped. Audyssey worked correctly and everything is setup as I wanted it to be. Thank you again for your explanation .
Did you run Audyssey after biwiring? If so, it probably increased the trim levels for each channel. That would make the system louder at the same scale on the MV than it was previously.