You want to run the left and right line outputs of your 'home theater' preamp into a stereo line level input of your 'music' preamp. When listening to music, you just select on your 'music' preamp whatever source you want, adjust the volume and enjoy. When watching movies, select the line input on your 'music' preamp that corresponds with your 'home theater' preamp. The only thing you will need to do is mark a "calibrated" position on the 'music' preamp's volume control so that you can set it to that when watching movies, and use the 'home theater's' volume control to set overall volume.