Digital BW, The Print

Some very quick thoughts. If you are comparing histos make sure the image cache prefs are identical for both PS versions.
Are there multiple versions of your destination space on your computer? Not only in your colorsync profiles folder, but Sys/
App support/Adobe/color/profiles/recomended.
Is PS6 using one and PS7 another? It's possible they could have been altered a touch over time. Get info in multiple versions 
to see. Make sure both destination spaces are the identical profile before assuming the conversion is at fault.
Tyler