Hello Keith,
For some reason the hardware does not support MACsec but take a look at this new little buddy:
https://cloud.kapostcontent.net/pub/51bac007-8b11-43c7-8522-fcb2f65f94ab/lrm-slash-macsec-adapter-data-sheet
It is to be working with EXOS 30.1 and for X590 with EXOS 30.2. I don't know release date for 30.1 but for 30.2 I've seen May 2019 so 30.1 should be like Q1. 😉
Hope that helps,
Tomasz