That is pretty blotchy Rob. Levels/Curves seems to bring up the detail but also the colour noise. Have you looked at each sub in the set? Go throught them and see if some are obviously crap or maybe tighten up the quality checks in maxim to kick out the rubbish from the stack.
Also checkout
Annie's Astro Actions for gradient removal. I've recently heard of these tools and they seem to work and are cheapish, see attached examples. Disclaimer, I have not used these actions myself even though the actions where used on my example images here, so I don't know if you have to be a brainiac to use them or not.