Hi ScottishBullet,
I have since found a way of doing this - well to be more specific, I found someone who has worked in modx and is a very helpful developer.
He reconfigured my client’s site for me in about half an hour, so that it works exactly how i want it to, with each editor having their own pages viewable and them not being able to see other peoples pages in the manager.
I can highly recommend this developer, and the company he works for. Give them a call - the guy is called Nick Crossland, and the company RCKT
http://www.rckt.co.uk
I am surprised that I was told it couldnt be done, when it clearly can be done exactly how i want it to be done, in the current version of modx and still have all pages viewable publicly on the website.
Give him a shout if you need help - it worked for me.
Hope that helps,
Sam