So I wanted to adjust some old pictures (made with 5 infinite) with 6 infinite, but I noticed right away that some of the atmospheres didn't translate right.  Mostly the quality seemed dirty, and the shadows were darker.  I would submit some pictures to show what I mean but when I try I get an error, some for now I hope that someone out there has experienced this as well and knows what I mean.

Any help?

You didn't say which type of atmosphere you are using in Vue 6. You'll get the best results with Vue 6's new "Spectral Atmosphere".
 
I suggest you start a new scene with that atmosphere type and experiment until you understand it - then convert your old scenes to the new Spectral Atmosphere type - with it's beautiful clouds.

At the same time, you might want to practice with the Vue 6 metaclouds.

_jc  'Art Head Start' e-book: Learn digital art skills $19.95
'Art Head Start.com Free chapter, Vue tutorials, models, Web Tutorials Directory.