Each radio has panadapter and slice "resources". The FLEX-6400 has 2 slice and 2 panadapter resources. They can all be used at the same time and on whatever frequency you want (within 100 kHz to 65 MHz).
For example, you can have two panadapters open with two slice receivers in one panadapter and none in the other panadapter. This configuration would be good for working split and monitiring a different band for activity.
Or you can have one slice receiver in each panadapter and work two bands while using digital mode software like WSJT-X.
And yes, each panadapter can show up to 7 MHz of spectrum at a time. The can overlap too, as the resources are independent.