Yeah @caphill has it right. You have it backwards. Even if your stereo pre doesn’t have a HT bypass, just hooking up the front L/R outputs from your prepro to an unused line input on your stereo pre is all that’s required. Set the balance for multichannel with the prepro hooked to your stereo pre so that 12:00 on the stereo pre balances with your multichannel setup (12:00 only because it's easily and pretty accurately repeatable by eye) and you’re done. Really, that’s it.
The bottom line is this -- for 2-channel listening the prepro is completely out of the loop and ONLY the stereo components are involved in playback. It’s a wonderful thing really. All you have to do is change the input on the stereo pre and your system switches completely from multichannel to a pure 2-channel system. If this is still confusing or seems impossible, just ask. It’s not an intuitively obvious thing. The only downside if you don’t have a HT bypass on your stereo pre is that when you switch from multichannel to stereo you need to turn the volume back down from 12:00 so the volume doesn’t blow you out of your chair. If you have a HT bypass this is a non-issue.
The bottom line is this -- for 2-channel listening the prepro is completely out of the loop and ONLY the stereo components are involved in playback. It’s a wonderful thing really. All you have to do is change the input on the stereo pre and your system switches completely from multichannel to a pure 2-channel system. If this is still confusing or seems impossible, just ask. It’s not an intuitively obvious thing. The only downside if you don’t have a HT bypass on your stereo pre is that when you switch from multichannel to stereo you need to turn the volume back down from 12:00 so the volume doesn’t blow you out of your chair. If you have a HT bypass this is a non-issue.