Jeffe is right on. In the three-way switch in the back, "cap coupled" and "direct coupled" are the two options for using it "separated," as you will be. For me the "cap coupled" option changes the output DC offset by quite a bit. You really don't need it if you're certain that the CA-F1 is not putting out any DC. Using the "direct coupled" option is best if you can do it, since it has no input capacitor. Test the preamp first, though, to be certain.
Tell us how it sounds, if you don't mind, as compared to the AU-919 preamp section.