As @imhififan said:
you can simply use a line level source a/b switcher on the Outlaw 2160II pre-out/main-in jacks to get the job doneThis is correct. However, you should pre-select a volume setting to use when you run the HT auto-setup on your HT system, and choose that pre-determined volume setting when you select/listen to HT in the future. This way your front L&R speakers will always be set correctly as they were when you ran your setup routine.