A: There are a few different ways to accomplish this. For direct-recording/split monitoring, use the direct outs 1-8 on theCR1604-VLZ® to the inputs 1-8 on the ADAT. Outputs from the ADAT should go into the line inputs of channels 9-16 (notice the handy TRACKS 1-8 at the bottom of those channel strips?) In this scenario, channels 1-8 are for recording, channels 9-16 for tape monitoring.
A modified version of this would to use SUBGROUPS out 1-4 for tracks 1-4 inputs, and the direct outs of channels 5-8 for those corresponding track numbers. This allows for printing effects to tape (via aux 3 return options) and multiple input channels to tracks (grouping drums, etc.)
A third option is to double-buss groups 1-4 with a splitter-cable adapter, sending sub 1 to tracks 1 and 5, sub 2 to tracks 2 & 6, etc. Also, the ADAT has internal normalization, which allows any signal brought into the first two channels to reach any of the other pairs. Just route all signals to subs 1 & 2 and track away (but only two tracks at a time.) In all these scenarios, use the line inputs for channels 9-16 as tape returns.