Well Tony
That's actually quite a reasonable image!
Can't believe the flat you described actually helped.???
Is this a crop from the original?
More colour is begging to come through but what is there looks quite balanced, well done. Do you know how to use layering in Photoshop? Layering will allow you to bring out the core detail.
Adjust levels and curves so that you have two versions of the M83 image, one that shows the detail in the core, the other with the core burnt in but showing the outer fainter bits. Now open both versions in photoshop, chose the detailed core version and select all and then copy and paste it onto the burned out core version. Now lasso the core region, feather 20 pixels, then select inverse and then press delete. This will basically paste the detailed core onto the burnt out core version and have the faint outer stuff as well!
Hope that was clear...?
Mike