Yes. With one exception. Both the Rialto 400 and 600 will NOT sum the left and right input when put into mono mode. It will derive the mono signal ONLY from the LEFT input.
On the Rialto 400 there is a switch on the bottom of the unit to switch between Mono and Stereo.
On the Rialto 600, you would flip the “Bridged” dipswitch.