Marantz PM 8003 v Rotel or NAD sperates

The first thing I would consider, is the companies you list, are all known for making integrateds. They do make separates, but I don't think they would a very big step up in terms of sound quality. I think the best thing you can do, is to go audition some new gear, but don't pre judge it based on the design. Just pick the one that sounds the best, regardless of design.

After reading your 2nd post, I realized that I didn't fully understand your first. Now that I do, I can't see how anyone could answer your question in any meaningful way. You have the NAD and Rotel separates and used to have the 8003. Its highly unlikely any of us has ever owned this combination of gear. If you're having a difficult time evaluating these components, how can any of us do better? At best, we would just be guessing.