Control Logix chassis as RIO to Control Logix

Is this possible? I was told that there would need to be a PLC in the Remote Rack??? Why would you want a remote I/O rack with it's own PLC???

Do you mean "RIO" as the remote I/O protocol or as remote I/O?

Of course you can have I/O remote to the CLX rack. Using Ethernet I/P or ControlNet for example.

I might add, only EtherNet/IP or ControlNet.
For a CLX platform Universal Remote I/O communications, the remote chassis could be only 1747 (SLC), 1771 (PLC5), 1794 (Flex) or any other Generic Remote I/O hardware.
The OP is correct: you cannot Universal Remote I/O control a remote 1756 chassis.

The acronym "RIO" or just the phrase "Remote I/O" has a very specific meaning in the Allen-Bradley world; it refers to the 1980's vintage Allen-Bradley Universal Remote I/O protocol, and to the characteristic blue-jacketed cable that was used with that protocol.

This is the "blue hose" twinaxial cable that was used to connect I/O chassis and devices to the old PLC-2, PLC-3, and PLC-5 controllers.

This old technology doesn't have the speed or sophistication to carry the sort of data a 1756-series I/O module needs, so there is no "RIO Adapter" for the 1756 series chassis.

As mentioned above, ControlNet and EtherNet/IP are the protocols that are used to connect I/O chassis to the ControlLogix family controllers. No CPU is needed in the remote chassis, just a 1756 series network module like the 1756-CNBR or 1756-ENBT.