What are the specifications of the terminals for SEND/RETURN (SEND FX EXTERNAL, MASTER INSERT)?

Both SEND/RETURN terminals are TS type (unbalanced).

Connect these terminals to the input/output terminals on external FX units.

When they're connected to only the L (MONO) of a RETURN terminal, the sound input to L (MONO) is also input to (R).

When connected to only the L (MONO) of the SEND terminal, mono audio is output.