Yes, I've been thinking along those lines as well Rob. But for the time being i think I've solved the problem ... for the time being.
So here's a quick repro, but this time with colour. I've cropped it a bit as well to improve the balance of the image. Quite happy with this now
edit:I'm also quite happy that the slight haze to the lower right of M66 (top) is real and not some image artifact. I spent a bit of time trying to process it out in the first image cos I thought it wasn't 'real'
