I cam across this problem a few days ago and resolved it yesterday with the help of Dylan Watson the creator of Monogame .Extended himself, I would like to share this knowledge with everyone.
P.S. If you need the other Mono.Ext. goodies do the same like you did to install the MonoGame.Ext. file.
Doing God's work, man.
Great work mate. I'm always in favor of doing things to help others
Just one correction I noticed...
If you install the MonoGame.Extended package it should install NewtonSoft.Json automatically for you. So you should be able to skip step 5.
True. But I included that step due to some having problems like tis one. http://community.monogame.net/t/having-trouble-with-succesfully-installing-monogame-extendeds-packages/9037"Leve no stone unturned.."