Thank you for responding to my question, Guy and Madskp. I may have gotten lucky. I found a new-old-stock MCL 2 Expander on eBay.
New questions come to mind (regarding newer MasterLink products) after researching the MCL2 expander and refreshing my memory on the X-tra speaker kit. I’ll post a new question in the forum for the benefit of other members. Thank you again for your help.