... the light from an umbrella is different fromthe light from a sofftbox.
And the llght from silver umbrellas is different from the light from white umbrellas.
And sometimes the light from a silver softbox differs from a white softbox differs from a golden softbox.
Oh, and I think size matters. the bigger the softbox, the softer the light. Same with umbrellas.
And distance matters.
The farther the softbox, or the umbrella, the sharper thelight, but also the less the falloff fromfront to back.
Combine softness and falloff desired with size and distance, and you can either organize your subject to be lit the way you want, or organize your lights to light the subject, in whatever manner it is organized, in a manner you like.
Multiple umbrellas can be placed fairly easily so they overlap smoothly, to light a big area. The miracle of feathering.
And it is a lot harder to arrange multiple softboxes to overlap evenly.
That said, softboxes drop off faster, and that can be your goal.
So... hard as it may be for someone who buys expensive cameras to comprehend, the key to lighting groups is not to be found by askinga question lioke this one.
It's to be found by deciding on the lighting, and then getting the equipment.
When in doubt: yeah, the Photek and the Easy-box or whatever it is called are not bad starts.
I use Photek umbrellas, mostly, five feet and three feet, and a 2x3 foot Multidome that I alsomost always use with the white inserts -- but with real flash units.
For Canon flash -- sort of like your Nikon flash, I use a two foot Photoflex umbrella on a light stand, by itself, or with a Fong Lightsphere.
And I'm thinking of buying both the Sftlighter and the Easybox, so you are ahead of me.
LINE OF SIGHT; if it does not work easily, seee about taping some foil to the back of the box, reflectinglight toward the flash units sensor.
BAK