The MS600 is described as having SL output, the HD621 as having MMHR over RJ45. What is the difference? Can I plug both into a G61R with a single CAT style cable?

Btw, I am thinking of replacing my aging G68 with a G61R, second time it broke. The web site shows the G61R as having SPDIF outputs, but my dealer told me SL and the manual agrees. Right?

Music room: 818v3, DSP8000SE, Roon/Intel NUC, microRendu/LPS-1 into Geek Pulse Xfi into Audeze LCD-3
HT: G61R, HD621, MS600, Oppo, Avantgarde Solo
Library: MS600, Bel Canto, Mark & Daniel
Other: SonicOrbiter, GeekOut, Audeze EL-8