Hi Kevin,
An oversight on my part. I found the 444 10 bit option way down at the bottom of the menu.
The quality is definitely a lot better, however a 1 minute file ended up being 2.49GB.
I believe ProRes is a mac specific format and I'm running windows, so I wasn't able to try your second option.
Steven, I've uploaded the same file I've been working with which you should be able to find here:
https://app.box.com/s/u9lo455ydn8qqtknbab5
hopefully you'll have better luck than me.
Now that I can see it's not impossible with the DNxHD 444 settings, I'll continue with my editing and I'll work out how to store and play the exported file afterwards.
thanks