Well how about that. The 80.1 and 70.1 do allow bridging of the front and surround back speaker channels. From the 80.1/70.1 owner's manual:
"Bridging the Front Speakers"
"The FRONT L/R and SURR BACK/ZONE 3 L/R terminal
posts can be used with front speakers and surround
back speakers respectively, or bridged together to provide
almost double the output power for the front
speakers.
When bridging is used, surround back speakers cannot
be used.
For bridging, the positive (+) FRONT L/R and SURR
BACK/ZONE 3 L/R terminal posts are used, but the
negative (-) FRONT L/R and SURR BACK/ZONE 3
L/R terminals are not.
Once you've completed the bridging connections
shown below and turned on the AV receiver, you must
set the Speakers Type(Front) setting to BTL to
enable bridging (see page 54).
Notes:
Use only front speakers with an impedance of 8
ohms or higher for bridging. Failure to do so may
seriously damage the AV receiver.
When using bridging, make sure that your front speakers
can handle the additional power."
My original comments still hold, however, in that the actual total power available in this configuration will be constrained by the AVR power supply capabilities. How much of a benefit this configuration will provide is debateable.