I am not sure why a "pass thru" connection would be desireable. I would suspect one would have better sound quality in the home theater mode by using the AVA preamp's line stage to drive the left and right front main amplifier and speakers. In general, the line outputs of the surround sound unit will be very limited in slew rate and current drive capabilty, and will be much happier driving into a resistive 47Kohm load of the AVA preamp than trying to drive whatever the imput impedance of the power amplifier is, along with the distributed capacitance of that load. A typical linear op-amp as used in the line stage of the processor is a 5 milliamp peak current device, and is subject to thermal feedback distortion internally too, and probably cannot drive the interconnect to the power amp and its associated load without saturating. Of course, many high priced interconnect cables make the capacitve load worse, and you can obviously hear that effect, but its not an effect you want to pay extra for.
Frank Van Alstine