Home theater bypass

If you want to use the Mac 275 for both stereo and HT duty, there will be two ways for connections:
1. Use a line level source selector connect to Mac 275 input to select the output from cj preamp or Onkyo 805.

2. Connect the Onkyo 805 front R/L preout to cj pv1 one of the line level input (not the phono) and set the cj volume control to unity gain position during HT playback.

To find the cj volume control at unity gain position:
connect the cj preamp main output to Onkyo 805 one of the analog input (i.e. CD input),
connect the cj preamp monitor or tape out to Onkyo 805 another analog input (i.e. AUX1 input),
connect a cd player to the cj preamp to play some test tone,
switch between the two input on Onkyo 805 and adjust the volume control on the cj preamp until both input getting same loudness/SPL.
Mark that volume control position on the cj preamp front panel, it’s the unity gain position.

With that type setup which preamp controls the sound to the amp?

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