NEC used to make an M13 mux, the RC-28D. I don't know if it is still in production, but it was a nice compact unit. This is a picture of it:

https://www.teledonsolutions.com/Imgs/products/item_sales/ThreeNEC_RC28D_M13_Multiplexers.png

Our old switch site used them and they gave us very few problems.


I Love FEATURE 00