It’s because the OP’s speakers are 4-ohm, and the Elicit is rated for 4-ohm operation, while the Marantz is not.
dvon, it’s hard to say if you need an outboard amp for your new center speaker. With the Marantz not having to deal with front left and right speakers, it may well do fine driving the center. Just hook it up and see what happens. If it plays as loud as you want and the Marantz doesn’t shut down, then you’re good to go.
Regards,
Wayne A. Pflughaupt