You want a preamp with "HT bypass" mode. The preamp would be connected between the Marantz 8805 and left/right chanels of the McIntosh 8207 amp. When you switch the preamp to the bypass input, it essentially connects the 8805 directly to the amp, allowing you to do any movie/streaming as normal.
When the preamp is switched to another analog source, it would just play that source (such as DAC or turntable) through it's normal preamp gain stage and out to the left/right channels of the McIntosh amp.
When the preamp is switched to another analog source, it would just play that source (such as DAC or turntable) through it's normal preamp gain stage and out to the left/right channels of the McIntosh amp.