Here is some information from Crutchfields website. It appears this model does not have A/B option for your mains. However, it does offer an A/B option for your surround terminal. Reading below it sounds like this is for people that want the best of both worlds, movies and music. One discussion that comes up around here a lot is using the Qs8's for music (DVD-A and SACD). Most people like to use direct radiating speakers (bookshelves) versus the Qs8's. This option would let you use Qs8's for lets say surround channel A, and also direct radiating for surround B (when your listening to SACD's for example)
Also, if you read below, it mentions that you have the option to use your back channel for Zone 2 or 3, however, the back channels will not be available for 6.1 or 7.1.
To answer your question, I believe you can just hook up one surround to the back channel (for ex. 1 Qs8) as for the most part currently there is no DVD's that are done in 7.1 or above anyway. However, not sure what will happen in the future as this material starts to become available...
Dual Surround Speaker Mode: The AVR-3806 provides the ability to connect two different sets of surround speakers, and place them in the appropriate locations in your home theater room, so that you can enjoy both movie soundtracks and music listening, with optimum results and no compromise. If you play one pair of surround speakers at a time (Surround A or B), the minimum impedance of the connected speakers is 6 ohms. If you play both pairs of speakers simultaneously (Surround A + B), the minimum impedance of the connected speakers is 8 ohms.
Multi Zone/Multi Source Operation: This unit provides a Multi-Zone Output function and a Select function that let you output different sources to multiple zones. Multi-room Zone 2 can have a pre-amp output along with a composite video feed. You can make the Zone 2 Pre-amp output variable or set to -40dB or 0dB. Multi-room Zone 3 can have an independently selected audio source output with a fixed pre-amp output. The receiver's Power Amplifier Assign function lets you assign the 2 Surround Back amplifier channels to instead drive a pair of speakers in Multi-room Zone 2 or 3 with 120 watts per channel. When the amplifier channels are assigned to Zone 2 or 3, the receiver can still provide 5 discrete amplifier channels to drive all speakers in a 5.1-channel surround configuration.
Randy
