If connect the Onkyo 805 front R/L preout to one of the line level input on cj pv1 and set the cj volume control to a fixed position during HT playback, the cj preamp act as a pass-through and the Onkyo 805 do all the control (i.e. select input source, surround mode, volume ...)
http://daveayers.com/Audio_Diagrams.htm
http://daveayers.com/Audio_Diagrams.htm
perhaps easier method from a practical standpoint is to use the 12:00 position on your CJ as the reference point for the input from the AVR and then use the AVR to set the correct volume levels for each channel. This method doesn't find unity gain for the CJ, but it avoids having to mark the proper volume level on the faceplate of your stereo preamp+1 soix