External Clock with Marantz SA-11S2?

I just purchased a Marantz SA-11S2 from another member here. So far I'm quite pleased with the sound, both on SACDs and redbook.

The Marantz has an input for an external clock, a feature I've never seen before. I have installed an upgraded internal clock in a more basic player before, and heard some improvements.

Has anyone used an external clock with the Marantz, and if so, what did you use and what did you hear?