There's a fairly consistent standard for the "stud" mount at the top of most lightstands, and the umbrella mount usually comes with one stud with male 1/4" (aka the tripod mount under your camera) and 3/8" (studly size for many tripod heads mounting on tripod legs) threads, and another stud with female 1/4" and 3/8" sockets. That gives you extra options when you want to mount a PW, etc.
Pick a softbox that does NOT have a specific mount, in other words it just has rods. Then pick the corresponding "speedring" to suit either your Einstein, one speedlight, or 1-2 speedlights. Take a look at http://profoto.com/us/products/light...dring-adaptors for one example - it allows Profoto softboxes to mount on many brands of lights, though I can't tell if the AlienBees model would work on an Einstein. This way, you just change out the speedring to suit the lights you're using, and keep the same softbox.
The challenge in doing the shots you showed comes down to the power of speedlights and the light lost while going through a softbox. You're going to have to limit yourself to less than sunny conditions, never with big groups or possibly even families >3 people, etc. - It might work, but you're going to need to become an ace at balancing ISO/aperture/shutter to keep the ambient at bay.





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