Connect the AV front L&R outputs to your stereo bypass inputs. Check for consistant phase between the stereo and AV outputs. This can be done by connecting only one channel through the stereo preamp and the other through the AV amplifier and making sure you have a strong central image. If you don't you need to reverse the terminals of the front left and right speaker connections.
Once everything is hooked up correctly with the proper phase you then adjust the levels of the front speaker for consistent output volume with the rest of the AV system.