Usually the only output connections on an amp are the speaker terminals, not phono. Trying to connect two integrated amps together is a definate no no and could cause serious damage to your equipment.
The only way that you can connect the tuner to both amps is to use a phono splitter at the tuner phono output and run seperate feeds to each amp.
You need two of the following from your tuner:

You can get all you need
here .
As far as Marantz owners manuals are concerned the nearest I can find is the 4001.
Manuals ( click on pic of amp for details page then select "Product Downloads" ).