The main reason a center channel sounds better on movies is that they tend to use it primarily for the voices in order to "bring them out" (eg higher volume, closer miking) and these can easily be correlated with the folks being portrayed, which tend to be center staged.
The most straightforward way to get what you want would be to buy an older AV preamp with a pass-thru. Use it for movies, keep your current preamp, and use it for your stereo listening with no audible deterioration. Your sub, if it has both line and speaker inputs, could use the line input from your AV receiver, and the speaker inputs you are now using for stereo music.
The most straightforward way to get what you want would be to buy an older AV preamp with a pass-thru. Use it for movies, keep your current preamp, and use it for your stereo listening with no audible deterioration. Your sub, if it has both line and speaker inputs, could use the line input from your AV receiver, and the speaker inputs you are now using for stereo music.