Home theater bypass

It depends.  When you're doing surround the AVR controls the volume, but for 2-channel not only does the stereo pre control the volume, the AVR is COMPLETELY out of the playback chain.  This is the real benefit of this setup.  Instead of swapping cables to switch between stereo and multichannel you just change the stereo pre to the input that takes the L/R preouts from the AVR and set the CJ's volume control to the proper reference volume level and you're done. 

BTW, while the method by @imhififan is maybe the more accurate way to go, another and 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.  Hope this helps, and enjoy your new setup!  I did this for years before I got a dedicated listening room and it was awesome. 

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

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

I like the schematic but I have a question. The passive pre is the cj the amp is the Mac receiver than what is the CDP where does it connect on the cj. Please excuse all the questions but I am still learning and I don't want to blow anything up. Many thanks 

You connect the CDP to any line level (non-phono, let's say the "tuner") input on the CJ and the L/R preouts from the Onkyo to another line level (let's say the "ancillary") input also on the CJ.  When you want to listen to 2-channel you choose the "Tuner" input on the CJ and when you want to do surround through the Onkyo you switch the CJ input to "Ancillary" and adjust the volume on the CJ to the reference level that keeps the L/R speakers balanced with the center/surround speakers.  That's basically it.  Just to be clear, only the preouts from the CJ go to the Mac 275. 

https://www.computeraudiophile.com/uploads/monthly_2013_09/58cd96b7e0681_HomeTheaterBypass.JPG.02904...
In the schematic, CDP is a compact disc player (CD player), passive pre is the cj and amp is Mac 275 and receiver is Onkyo 805.

Maybe this schematic give you a better idea:
http://daveayers.com/Audio_Diagrams.htm