Okay, so here is what I am attempting to do.

New 17" i7 MBP as my main edit station.

I would like to add a 27" iMac to use as a 2nd monitor in target display which I know I can do.

I would like to use the 27" iMac as my secondary transcoding station.

I would like to use Thunderbolt drives on both systems.

So the idea is

17" MBP > Lacie 2Big thunderbolt 4TB>Lacie 2Big thunderbolt 4TB>imac 27" display

at the same time I would like to hook up 2 additional Lacie2Big Thunderbolt drives to the iMac for it's own storage.

Any idea if this can be done? Just not sure if or where the drives connected to the iMac will mount.